The truck hit the mine on Friday in the northern province of Oddar Meanchey - a former stronghold of Pol Pot's Khmer Rouge.
Theak Thea, a provincial police official, said: "A lot of mines were planted in those former battlefields and no one knows where they are until they explode."
Last November, an anti-tank mine killed 14 villagers travelling in the same area not far from the mountain redoubt of Anglong Veng where Pol Pot died in December 1998.
Cambodia's northern border regions are littered with millions of landmines, the legacy of nearly 30 years of fighting, which only ended with the final surrender of the remnants of Pol Pot's forces in 1998.
Mine-clearing teams have destroyed an estimated 1.6 million landmines in the last decade, but millions more remain and are responsible for hundreds of deaths and injuries every year.
Of more than 4,000 mine-related casualties reported between 2000 and 2004, more than 1,000 were children.