The explosion took place at around 4.00 p.m. local time (11:30 GMT), in the city's west, the sixth police district.
"The explosion took place on the road of Faiz Mohammad Kateb, near to general attorney's office in the area, and when the officers left the centre, a motorcycle bomb blasted", the source said.
Kabul police have confirmed the incident but have not provided any details about its nature and the casualties.