The militants came on a motor-cycle and opened fire on the three persons standing at Chandni chowk bus stop. They were waiting to board a pilgrim bus to Taftan in Iran, a police official said.
Two of them died on the spot while the third passed away in a hospital, he said, adding, the deceased were identified as Mirza Hussain, Asadullah and Mohammad Ali.
Meanwhile, Prime Minister Nawaz Sharif strongly condemned attack and extended condolences to the bereaved families.
Those killed belonged to ethnic Hazara Shiite community, the official said, adding, a search operation has been launched to nab the attackers.
Balochistan has faced violence by sectarian groups who frequently target the Shiites, who travel to Iran to see their holy places.