The bomb went off when a Frontier Corps vehicle was on a routine patrol on the national highway, said Mohammed Wasay, spokesperson for the para-military force.
Soldiers rushed to the spot and cordoned off the area after the explosion.
The four injured personnel were taken to a nearby hospital.
Awaran, near which the attack occurred, is among the worst militancy-hit areas. Last year a massive earthquake flattened 95 per cent of the region.
The banned separatist Baloch Liberation Front (BLF) is active in the area and often blamed for such attacks.