Majd Kayyal, a 23-year-old journalist for the Lebanese newspaper As-Safir, travelled to Beirut last month for a conference.
Although Lebanon bars Israeli citizens from entering, the Shin Bet said Palestinian officials in the West Bank gave Kayyal Palestinian travel documents that allowed him to enter Lebanon.
Kayyal was arrested last Saturday at the Israeli border on suspicion of being recruited by a militant organisation.
The Shin Bet said it dropped that suspicion, and is considering indicting him for travelling to Lebanon.
Israel lifted a gag order on the arrest today.