Mojtaba Mirtahmasb is an Iranian filmmaker and film producer. He is most famous for co-directing the illegal 2011 film This Is Not a Film with Jafar Panahi.

Mirtahmasb was born in Kerman, Iran in 1971. From 1992 until 1995 he attended the University of Art “Mojtame’-e Daneshgahiyeh Honar” in Tehran, studying Visual Art and Handicrafts. At school he was primarily interested in Shiite Rituals and Ceremonies, but also studied photography and filmmaking. After graduating he directed nine documentaries for the Islamic Art and Material Culture of Iranian Shiism in 1996 and 1997. The subjects of these films included calico making, the art of glazing, enamel work, Islamic tile work and Islamic needle work. During this period he also directed three short videos during his military service called The Story of Khoramshahr, Motherland and Stars. He has worked with such Iranian film directors as Kambozia Partovi, Mohsen Makhmalbaf and Siddiq Barmak.

In the Fall of 2011 Mirtahmasb and five other Iranian filmmakers were arrested by Iranian authorities for their participation in the BBC Persian's documentary on Supreme Leader Ali Khamenei. The Iranian Intelligence Minister accused the six filmmakers of "anti-national missions for the British Intelligence service's centre for psychological and secret operations, also known as the BBC." He was released in December 2011. In December 2012 This Is Not a Film was shortlisted as one of 15 films eligible for Best Documentary Feature at the 85th Academy Awards.