The gunmen opened fired at an armoured police vehicle when it was being driven from Hazar Ganji to Shalkot, police said.
Following the incident, the area was cordoned off and closed for traffic.
No one immediately claimed responsibility for the attack, but Sunni extremists have targeted Pakistan's Shia minority in past attacks.
Attacks on police personnel have become a frequent occurrence in Quetta and other parts of restive Balochistan province.