Some miscreants threw grenades at Pirano Mosque in Achini Bala area, a suburban locality of Peshawar in Khyber Pakthunkhwa, police said.
Three people were killed and eight others injured, police said.
The area is situated at the border between Peshawar and Khyber Agency.
District Peshawar police and security forces rushed to the site, cordoned off the entire area and started a search operation to nab the assailants.