Mohammad Khan Qajar (Persian: محمدخان قاجار) was the khan (governor) of the Erivan Khanate from 1784 to 1805.

Mohammad Khan of Erivan belonged to the Qovanlu branch of the Qajar tribe. He was the son of Hoseyn Ali Khan of Erivan and a Christian woman from Tiflis (Tbilisi). He was twelve years old when his brother, Gholam Ali, was assassinated in a conspiracy after less than a year as Khan of Erivan. The conspiracy was the work of disaffected officials who had been sidelined by Gholam Ali in favor of his relatives; agents of the Georgian king Heraclius II (r. 1762–1798) of Kartli-Kakheti are also thought to have been involved in the coup. Mohammad Khan's mother served as his regent until he came of age.

In order to preserve his realm, he acknowledged the suzerainty of Heraclius II. He also rejected overtures from the Ottoman sultan, who promised assistance if he would ally with the neighboring khans against Heraclius, who had accepted Russian protection in 1783. He then faced a rebellion by supporters of his predecessor, Gholam Ali Khan. The rebels caused devastation and were defeated only after Heraclius's troops arrived to assist Mohammad Khan. In 1785, Umma Khan of Avaria, encouraged by the Ottomans, raided Heraclius's kingdom with a 20,000 strong army, causing great panic in the Erivan Khanate. The khanate's inhabitants twice fled their homes to take refuge in fortified places. Although Heraclius soon made peace with Umma Khan, various forces in the Erivan Khanate took advantage of Mohammad Khan's weakness to vie for power, causing further devastation in the territory.

In 1795, Agha Mohammad Khan Qajar (r. 1789–1797), who in the previous years had established his rule over much of Iran, began preparations for a campaign to restore Iranian control over the South Caucasus. As news of the imminent campaign spread, many inhabitants of the region fled towards Georgia, with many dying of disease or starvation. Mohammad Khan prepared for a siege, reportedly stationing 7,000 soldiers in the Erivan Fortress and storing enough supplies to last seven years. Agha Mohammad Khan's 50,000 strong army crossed the Aras in June 1795; a detachment of 20,000 men, commanded by Agha Mohammad Khan's three brothers, was sent against Erivan. Mohammad Khan moved the population of the city of Erivan and its surroundings to the citadel. The siege of Erivan began in late July 1795 and lasted thirty-five days. During that time, the enemy army caused great destruction in the settlements of the khanate. The population of Erivan showed fierce resistance and hoped that Heraclius would arrive with help, although he was focused on defending his own kingdom and was unable to do so. Mohammad Khan delayed his response to Agha Mohammad Khan's demand for submission, but he eventually decided that further resistance was futile. He accepted Agha Mohammad Khan's overlordship and gave his wife and newborn son as hostages.

In order to supervise Mohammad Khan, Agha Mohammad Khan appointed one of his men as commandant of Erivan Fortress, supported by 400 soldiers. During the Russian expedition into the Caucasus in 1796, Agha Mohammad also sent his brother, Ali-Qoli, to Erivan; according to Vardan Grigorian, this was to block Erivan's increasing aspirations to accept Russian rule. It is likely that the Shah found out about Mohammad Khan's communications with the Russian military, in which the Khan asked for assistance to free himself from Iranian rule. Mohammad Khan sent one of his men with gifts to the Shah in order to regain his trust, but the delegate was received badly and returned.

In early 1797, the Shah was preparing another campaign in the South Caucasus, as Shusha in the Karabakh Khanate remained unconquered. He demanded troops and artillery from Mohammad Khan for the campaign. In January 1797, Mohammad Khan sent a letter to Count Valerian Zubov, the commander of the 1796 expedition, asking for help; but the Russian troops had received orders to leave the South Caucasus since the death of Catherine the Great and the accession of Paul I (r. 1796–1801), and Mohammad Khan received a negative answer. According to Yegor Khubov, an Armenian go-between for the Russians and the khans of the Caucasus, the Shah ordered Mohammad Khan to come to the capital for Nowruz and to bring his treasures with him. When Mohammad Khan, along with Kalb-Ali Khan Kangarlu of Nakhichevan, arrived at the royal court with rich gifts, the Shah accused them of treason. According to Khubov, the Shah would have had Mohammad Khan killed if some of the Shah's high-ranking officers had not interceded on the Khan's behalf. Kalb-Ali Khan was blinded on the Shah's orders, and Mohammad Khan was imprisoned and his property was confiscated. George Bournoutian writes that it was because of their shared Qajar ancestry that the Shah spared Mohammad Khan (Mohammad Khan was Agha Mohammad's maternal cousin).

Agha Mohammad Khan was killed in Karabakh in 1797, and his successor, Fath-Ali Shah Qajar (r. 1797–1834), sent Mohammad Khan back to Erivan to continue as its governor. In late 1798, Fath-Ali Shah gave Mohammad Khan a firman (royal decree) permitting him to rule Erivan, demanding in exchange a large sum (equivalent to 20,000 rubles) and the giving of hostages. As Mohammad Khan did not want to pay the sum, he began negotiations with Georgia. His recalcitrance provoked Fath-Ali to send the crown prince, Abbas Mirza, and the commander Soleyman Khan against him and the rebellious khan of Khoy in mid-1799. Mohammad Khan sent his troops to join those of Khoy, but the khans were defeated and Khoy was conquered. In the spring of 1800, Abbas Mirza's army set out for Erivan from Tabriz, despite Russian attempts to dissuade Fath-Ali from another campaign in the South Caucasus. Mohammad Khan again appealed to the Russians and the Georgians for assistance, and both King George XII of Georgia and the Russian minister Kovalensky promised to help. The Qajar army besieged Erivan, but because of their lack of artillery they were unable to take the fortress; the Khan's troops even made several sorties and attacked the besiegers. Eventually, Mohammad Khan agreed to pay a fine and Abbas Mirza lifted the siege.

Less than a month after Abbas Mirza's departure, Mohammad Khan sent troops to take Shoragel from the Georgians. He was not deterred when George XII sent a force of 400 men commanded by Pavel Tsitsianov to protect the region; the Khan's troops defeated the Georgian force and captured and destroyed the fortress of Shoragel. Mohammad Khan also desired to conquer Pambak, which had earlier been granted to him by Agha Mohammad Khan. To prevent this from happening, Russian troops approached the border of the Erivan Khanate, and Mohammad Khan was forced to abandon his plan. According to Grigorian, Mohammad Khan's real goal was to be independent of the Shah, the Russians, and the Georgians—his professed desire for Russian protection notwithstanding. Although Mohammad Khan was not noted for being courageous, he was skilled in politics and maintained contact with the Russians and Ottomans, while also guaranteeing Iran his allegiance.