Lebanon's Foreign Affairs Minister Fawzi Salloukh says people were instructed to leave after an embassy official received a call saying the building would be bombed.
Some media reports say the threat was called in to a foreign news agency, and that staffers there warned the embassy.
The building has not been attacked. But, according to Kuwait's official news agency KUNA, the threat alone has prompted Kuwait's foreign ministry to urge its citizens to postpone any travel plans to Lebanon.
Tensions are high in Lebanon, as the nation's political crisis continues without resolution.
Lebanon has been without a head of state since November, and an often-postponed parliamentary voting session to elect a new president is set for February 26.
Lebanon's pro-Western governing coalition and the Syrian-backed opposition have agreed on an Arab League plan calling for the election of army chief General Michel Suleiman. But they differ on how to form a new national unity government.
Some information for this report was provided by AFP, AP and Reuters.