The An-Nahar newspaper said the military-grade Grad rockets, which were found in the Sunni village of El-Qaa, were aimed at nearby Hermel, a stronghold of the Shiite militant group Hezbollah.
The army said military police had opened an investigation.
The conflict in neighboring Syria has inflamed sectarian tensions in Lebanon, with Hezbollah sending fighters to back President Bashar al-Assad’s forces and many Sunnis offering sympathy or support to the rebels.
Al-Qaa and the nearby town of Arsal have been key transit points for arms smuggling by the rebels and for refugees fleeing the fighting.
But the traffic has slowed in recent weeks following a Syrian army offensive on the other side of the border in which it has recaptured a string of towns from the rebels.
Elsewhere in northern Lebanon, a man was killed on Friday night in demonstrations that erupted after the arrest of a local man in connection with a double suicide bombing in southern Beirut on November 19.
In a statement, the army said it had returned fire after demonstrators shot at troops trying to reopen a road blocked by the protest, killing one person.