The latest bombing, in a country destabilised by the civil war in neighbouring Syria, was the third such attack in recent weeks in Hermel, a predominantly area of Lebanon near the border with Syria. Fifteen people were wounded.
It followed a suicide attack in Beirut on Wednesday, targeting the Iranian cultural centre that killed eight people. A radical Sunni group said it had carried out that bombing as a reprisal for the military involvement of Hezbollah and Iran in the Syrian war.
There was no immediate claim of responsibility for Saturday's attack. The bomb was set off when soldiers at the checkpoint became suspicious of the man in the vehicle, a Jeep Grand Cherokee, the sources said.
Hezbollah, an Iranian-backed political and military movement, is fighting alongside President Bashar al-Assad's forces against predominantly Sunni Muslim rebels in a conflict that has exacerbated sectarian tensions in Lebanon.