Levies sources said that the bus caught fire shortly after the blast and the bus was severely damaged.
According to reports, the bus heading towards Quetta from Iran when it was targeted by a remote-controlled blast in Maustang.
The dead and injured were taken to a nearby hospital. Balochistan has been witnessing a sectarian rift and hundreds of people have lost their lives.
Levies sources said the bus was escorted by the paramilitary force and three personnel were also injured in the line of duty. They said unknown attackers also opened fire on the bus following the blast.
Deputy Commissioner Mastaung has confirmed the attack and told media three people had lost lives in the incident.