The attack near the eastern border town of Arsal came after forces loyal to Syrian President Bashar al-Assad routed rebels from two Syrian villages lying just across the border.
According to AP, the bomb killed three soldiers and wounded another four, a military statement said. Military helicopters rushed to rescue the wounded from the rugged mountainous area, said the army statement.
The Ahrar al-Sunna in Baalbek Brigade claimed responsibility for the bombing.
The group described the attack as a "heroic operation that targeted the crusader army in Arsal" in a message posted on Twitter.
The group said the bombing was to avenge the Lebanese army killing of a suspected militant during an arrest raid on Thursday, and for Hezbollah's participation in the Syrian conflict.