Among those killed and wounded were police officers attending prayers at the mosque.
The co-ordinated assault was the latest in a surge of militant violence near the border with Afghanistan where Pakistani Taliban militants have increasingly targeted police and other security forces as the government intensifies operations against them.
The bombing occurred in Kohat, a district in Khyber Pakhtunkhwa.
An attacker apparently rammed an explosives-laden vehicle into the mosque, provincial police chief Zulfiqar Hameed said.
At least seven armed gunmen also attempted to enter the police compound and exchanged fire with officers.
Six of the gunmen were killed, according to police, who said one suicide bomber attacked the nearby office of an intelligence agency.
The police compound housed counter-terrorism police, who had carried out operations against militants across the province in recent years.
Most of those killed were police officers, hospital officials said.
Bilal Faizi, a senior rescue official, said most of the dead and wounded had been attending prayers at the mosque.
Photos from the scene showed the outer wall of the police offices had collapsed and the mosque was badly damaged.
Smoke rose over the site after the blast, which witnesses and residents said was heard far away, followed by gunfire.
Inside the mosque, piles of bricks and concrete buried the floor, wires dangled from cracked walls and daylight poured through jagged holes in the roof while a ceiling fan hung above the wreckage.
Residents said the exchange of fire continued hours after the co-ordinated attack.
Prime Minister Shehbaz Sharif condemned the attack and expressed sorrow over the casualties.
He directed authorities to accelerate rescue operations.
No group immediately claimed responsibility for the attack but suspicion was likely to fall on the Pakistani Taliban, formally known as Tehrik-e-Taliban Pakistan or TTP.
The attack comes a day after a roadside bomb struck a security forces convoy in the northwestern Hangu district and killed six soldiers.
Government troops also conducted raids in various areas on Thursday and killed 10 militants believed to be members of the Pakistani Taliban, the military and police said.
