The vehicle was reportedly carrying government employees from nearby areas to the city.
At least 25 others have been injured, Pakistani media say.
A senior police official quoted by Reuters news agency said explosives were apparently planted inside the vehicle.
About 40 people were inside the bus at the moment of the explosion, he added.
Television pictures showed the vehicle partially destroyed and some of the injured being taken to a hospital.
Pakistan: Bus bomb explosion kills 15 in Peshawar
16 March 2016
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At least 15 people have been killed after a bomb exploded in a bus in the north-western Pakistani city of Peshawar, reports say.
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