The truck had brought the workers to a mine in the Harnai area of Balochistan province, where Pakistan is battling a separatist insurgency.
"An improvised explosive device was planted at the road side which exploded when truck carting coal miners reached the site," a paramilitary official said.
The official, who declined to be identified, added that it may have been a remote operated device.
No group has claimed responsibility for the attack.
The region's deputy commissioner, Hazrat Wali Agha, said 17 miners were in the truck when the bomb went off.
A doctor at the local hospital said two of the wounded are in critical condition.
Mineral-rich Balochistan, which borders Iran and Afghanistan, has been the scene of a decade-old insurgency by separatist ethnic Baloch groups. Islamist militants also operate in the area.
