It was the first time in three months that the two leaders had met.
Amin Gemayel, the former Lebanese president and prominent Christian leader, who is aligned with the governing majority, also took part in the three-hour talks in the parliament building in Beirut.
Discussions centered around the an initiative to elect a new president and the formation of a national unity government.
"There were some agreements on some topics and this makes me optimistic that there is wide room for [fuller] agreement," Moussa later said.
"But there are some matters which require dialogue between the parties."
He is due to return to Beirut from Damascus to continue his mediation.
Political crisis has engulfed Lebanon since the post of the country's presidency fell vacant in November.
Although both sides have agreed on who should become president - General Michael Suleiman, the army chief - the division of power in a new coalition government has not been established.