"At around 8:30 am (0530 GMT), a drone belonging to the Israeli enemy went down in the port of Tripoli, and the army has taken the necessary measures," the Lebanese military said in a statement, without elaborating.
A security official said the pilotless aircraft crashed into the sea.
"Fishermen had the impression a plane was falling down towards their harbour, close to the main port of Tripoli," said the source, who spoke on condition of anonymity.
An spokesman for the Israeli military refused to comment on the reports.
On June 21, Israel carried out an air strike in eastern Lebanon to destroy one of its drones that had crashed in the mountains outside the village of Saghbine.