The attack took place in the coal-rich Chamalang district, where clashes occurred in recent days.
The army says that separatist rebels are behind the attack.
Baloch rebels have been waging an insurgency for decades, fighting for greater political autonomy and a share of the province’s natural resources.
One report says the troops were attacked as they guarded a private coal mining venture in the area.
But the army spokesman is quoted by the Associated Press news agency as saying a three-vehicle convoy was attacked as it was travelling from Chamalang to Dukhi.
Balochistan, Pakistan’s largest and most sparsely populated province, is rich in minerals and has vast untapped deposits of oil, gas, copper and gold.
As well as a separatist insurgency, the province has also been affected by sectarian violence and Taliban suicide attacks.
Last month Pakistani Prime Minister Yousuf Raza Gilani said that development and reconciliation were the only ways to stop militancy in Balochistan province.
But correspondents say that there is a growing sense of frustration among unemployed youths in the province who are increasingly joining pro-Taliban militant groups or the separatist insurgency.