The attack occurred in Naseerabad district, 400 km southeast of provincial capital Quetta.
At least gunmen riding motorcycles fired at the two trucks, killing a driver. They then set a truck carrying a heavy NATO vehicle on fire.
The trucks, coming from Afghanistan, were headed for Karachi.
The NATO mission in Afghanistan is due to end next year and most of its military hardware will be flown out of the land-locked country or moved by road to the port city of Karachi.