"Two soldiers were killed and three wounded when a bomb exploded as a military vehicle was headed for Arsal," the army said in a statement.
Residents said the attack took place in an area on the outskirts of Arsal called Wadi Hmeid.
They said Lebanese military surveillance aircraft overflew the area after the blast. Security forces cordoned off the area, an AFP journalist said.
An officer had said earlier that the truck was probably hit by a rocket-propelled grenade.
Last month, it was the scene of a major battle between the Lebanese army and jihadists who had streamed across the frontier.
Extremists in Lebanon view the army as backing Shiite Hezbollah, which has sent thousands of fighters into Syria to support President Bashar al-Assad's forces battle rebels trying to oust him.