The official National News Agency reported the military intercepted a vehicle carrying Lebanese, Syrian and Palestinian nationals in Beqaa province. The men were found with uniforms used by al-Nusra Front, an al-Qaida affiliated group fighting against pro-government forces in Syria.
"The five detained [men] were heading in the direction of Syrian territories," the official news agency stated.
The U.S. State Department last year said al-Nusra Front was an alias for al-Qaida in Iraq.
Lebanon's national security is in jeopardy because of a spillover threat from the Syrian civil war. A bombing last week in Beirut was said to be in response to Hezbollah's role in the fight against rebels opposing Syrian President Bashar Assad.
Former Lebanese Prime Minister Saad Hariri last week said Hezbollah was posing a threat to Lebanon.
"What Lebanon is facing at present approaches the brink of existential danger and threatens Lebanon's message and the values of cultural and religious diversity," he was quoted by The Daily Star newspaper as saying.
Hezbollah was tied to the 2005 assassination of Rafik Hariri, the former prime minister's father.