A perpetrator drove a car packed with explosives into the facility. Several armed attackers then stormed an adjacent police building.
In addition to the many deaths, around 80 people were injured. Most of the dead were police officers, according to hospital reports.
A number of attackers were also killed in gunfire with police.
The mosque is located in the city of Kohat, in a province that borders Afghanistan to the west.
Authorities have not initially named anyone responsible for the attack. The region has seen many violent attacks in recent years that have been attributed to the Pakistani Taliban movement, the TTP, which has strained relations between Pakistan and the Taliban regime in Afghanistan.
