Al-Mahdi Muhammad bin al-Mutahhar (1275 - October 28, 1328) was an imam of the Zaidi state in Yemen who ruled from 1301 to 1328.
After al-Mutawakkil's death in Hajjah in 1298, al-Mahdi Muhammad claimed the succession, although the imamate was not strictly speaking hereditary.
When he acceded, the Sunni Muslim Rasulid Dynasty was still in a strong position, and dominated most of Yemen, including San'a.
A major battle was fought in Yemen on 26 December 1311 where the troops of the Rasulid Sultan al-Mu'ayyad Da'udsultan were crushed.
Upper Sheref and a number of other places were acknowledged as belonging to al-Mahdi Muhammad, who furthermore received 3,000 ducats per year from the sultan's treasury.