The suicide bombing took place on University Road, close to a parked police vehicle, Geo TV reported.
"At least six people were killed and 38 others were wounded in the bomb blast," a police officer said.
An earlier report had put the toll at three.
"The commissioner, who passed just a minute before on the road, was the target of the bombing, but he escaped unhurt as the bomber missed the target and struck his motorcycle into a passenger bus," a police officer was quoted as saying.
The suicide bomber's body parts were found at the blast site. However, it was not clear, immediately, whether he wore a suicide vest or the vehicle was rigged with explosives.
Officials estimated the explosives weighed up to six kg.
No group has yet claimed responsibility for the attack.