Several people were injured in the blast and shifted to the District Headquarters (DHQ) Hospital for treatment, according to police.
Police said the explosion occurred during Friday prayers and created a crater outside the mosque. Police personnel were among those injured in the blast.
An additional contingent of police was deployed at the Police Lines following the explosion, officials said.
Rescue officials said the blast severely damaged the mosque’s outer section and caused a wall to collapse.
Rescue teams were conducting operations at the site of the explosion, the officials added.
Meanwhile, authorities closed the Kohat-Hangu Road to all traffic following the incident.
The DHQ Hospital administration in Kohat also declared an emergency as injured people were brought in for treatment.