Bello-Indimi Zabarmari says the blast occurred Wednesday. He says the mine was planted as the extremists fled after trying to attack Khaddamari town outside Maiduguri city in Borno state on the eve of the Feb. 23 elections.
Zabarmari says the farmers defied soldiers' warnings not to use the road because they wanted to reach their cucumber farms.
He says four died at the scene and a fifth died at a hospital. A security source who spoke on condition of anonymity because they were not authorized to speak to reporters had estimated seven dead.
Nigeria's Boko Haram insurgency is now a decade old.