The explosion in the provincial capital Quetta's Satellite Town area occurred when people were assembling for prayers near the mosque.
"Four policemen were killed," he said.
Security forces cordoned off the area.
There has been sudden spike in violence in Balochistan in recent weeks.
The attack came two days after a terrorist attack on a luxury hotel in the coastal town of Gwadar in which five people were killed while security forces gunned down the three terrorists who stormed the facility.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)