The attacker, reportedly riding a motorcycle, detonated his explosives near the police van on University Road Monday morning.
The van was close to a bus stop and a crowded bus that was passing by bore the brunt of the blast.
Six persons were killed instantly and 38 injured people were taken to a nearby hospital. Two policemen were among the wounded.
Police and security forces cordoned off the area after the blast.
Superintendent of Police Muhammad Faisal confirmed the blast was a suicide attack. He said the limbs of the bomber had been found at the site of the attack.
The police vehicle was the apparent target but the bus suffered more damage, he said.
Peshawar Commissioner Sahibzada Anees' vehicle passed the site of the blast a few minutes earlier and he escaped unhurt, officials said.
University Road is one of the busiest thoroughfares in Peshawar. Several cars were damaged by the blast.
On Sunday, 12 people were killed and more than 40 injured in four bomb attacks targeting campaign offices and election meetings in Khyber-Pakhtunkhwa and Balochistan provinces.
The banned Pakistani Taliban claimed responsibility for two of the attacks.
Pakistan has witnessed a sudden surge in militant violence ahead of the landmark May 11 general election that will mark the first democratic transit.
Image: Relatives stand near a victim of a bomb blast at University Road in Peshawar on Monday
Photograph: Fayaz Aziz/Reuters