The mosque was targeted in Hayatabad area of Peshawar, capital of Khyber-Pakhtunkhwa.
At least three explosions and gunfire was heard when worshippers had assembled for the 'Zuhr' afternoon Friday prayers. The nature of explosions was not known yet.
So far, 10 people have been killed and over 60 others have been injured, police said.
There were also reports that some militants were still in the mosque and are still exchanging fire with security forces.
The attack is a reminiscent of the December 16 Peshawar school carnage last year that killed at least 150 people, including 136 students.
Late last month, at least 61 people, including children, were killed in a suicide bombing during Friday prayers at a packed minority Shia mosque in Pakistan's Sindh province, the deadliest sectarian attack to hit the country in recent times.