The raid was the latest in a string of cross-border strikes against Arsal. On January 17, shells rained down on the town, killing eight people, including five children.
A December air raid prompted the Lebanese army to fire back with anti-aircraft guns.
Arsal's residents support the revolt against President Bashar al-Assad, and the town has become home to thousands of Syrians who have fled the fighting.
Once dominated by Damascus militarily and politically, multi-sectarian Lebanon is deeply divided over the Syrian war, with Sunnis backing the Sunni-led revolt and Shiites largely supporting the Assad regime.