The ultras lobbed a grenade at Sherbagh police station of Anantnag town at around 9 pm, police said.
The grenade exploded near the main gate of the police station, resulting in minor injuries to three cops, the police said.
The injured policemen were taken to Anantnag district hospital for treatment.
No militant outfit has claimed responsibility for the attack which comes three days ahead of polling in the south Kashmir district.
Jammu and Kashmir has witnessed a series of militant attacks since the start of the polling process.