The grenade was fired by an assault rifle at the Helu barracks which had been targeted with a similar projectile last month. Police deployed around the barracks after the attack, the source said.
Four similar security incidents happened in the Lebanese capital last month, including most recently the October 25 detonation of a small amount of dynamite on a road running next to the Mediterranean, also causing no casualties.
On October 15, six civilians were slightly wounded when rockets hit a building next to the UN office and the prime minister's offices in downtown Beirut.
Police barracks were also targeted by grenades in two other October incidents that caused no casualties.
The Lebanese government recently decided to set up a network of surveillance cameras in Beirut and its suburbs, two years after the start of a spate of bombing attacks that mainly targeted figures who opposed Syrian domination of its smaller neighbour.
Among those targeted was former prime minister Rafiq Hariri, who was killed by a massive car bomb in the capital in February 2005.

Copyright AFP (Agence France-Presse), 2006