The killings came just two days after gunmen ambushed a police mobile van in the Pashtunabad area and killed four policemen.
Police said two brothers, Mohammad Rafique and Mohammad Naseeb, were killed when unidentified men opened fire at a barber shop on Mano Jaan Road in the Saddar commercial area.
In a separate incident, two people were gunned down by suspected terrorists in Quetta.
The shooting incident occured on the Double Road and security officials cordoned off the area soon after.
Meanwhile, in an ongoing search operation against terrorists in Quetta, security forces claim to have arrested 243 suspected militants in the Mahmoodabad area and recovered huge cache of arms and ammunition.