Another five people were wounded by Wednesday's blast in the remote village of Kharcha in the Baluchistan province, Abdul Samad Lasi, the district co-ordination officer, told AFP.
Lasi said: "Six people were killed and five injured when a minivan struck a landmine in Kharcha. The landmine was planted by miscreants."
Miscreants is the official Pakistani shorthand for ethnic Baluch tribal fighters who are waging a sporadic revolt against the government.
Lieutenant-Colonel Furqan-ud-Din, of Pakistan's paramilitary Frontier Corps, said, two women, three children and the male driver were killed in the explosion.
Ethnic Baluch fighters are demanding a bigger share of the vast but sparsely populated region's gas reserves and other natural resources, jobs in state projects and greater political rights.
The site of the explosion is 112km from the town of Dera Bugti, where security forces and tribesmen have been engaged in a month-long standoff.
Another landmine planted by fighters was defused on Tuesday by security forces at Pirkoh near Dera Bugti, Furqan-ud-Din said.
Officials say five soldiers have died since December; three of them when a landmine or roadside bomb exploded near a major gasfield at Pirkoh on 11 January.
Twelve suspected fighters died in a shootout after that blast, officials said, while the tribesmen say dozens of civilians have been killed in shelling by Pakistani forces.
Local tribesmen say the Pakistan
army attacks are killing civilians
The figures for civilian deaths were not confirmed by officials and have been impossible to verify independently.
The government launched its latest crackdown on the tribesmen in December after rockets hit the remote town of Kohlu during a trip to the region by Pervez Musharraf, the Pakistani president.
Islamabad crushed a tribal revolt in Baluchistan in the late 1970s. Trouble resurfaced in the area last year with sporadic clashes as well as attacks on government installations, railway tracks and gas facilities.