Local TV reported, without any official confirmation, that Abdul Aziz was arrested as he tried to sneak past police cordons with a group of female Islamic students wearing burqas.
The arrest comes amid threats of suicide strikes from Islamic students currently surrounded by security forces in the mosque, where around 12 people died in clashes with security forces Tuesday, according to local media.
Lal Masjid and some other districts of the Pakistan capital have been placed under curfew, with the police threatening to shoot anyone in possession of weapons. Interior Ministry troops have blocked several key roads in the city, and public transport has been brought to a halt.
The radicals inside the Mosque have called for the overthrow of President Pervez Musharraf and accused him of betraying Islam to the U.S. and the West.