Political challenge
Aridi did not say to whom he thought the weapons belonged.
The Lebanese government is facing a political challenge from a number of opponents, including Hezbollah.
The standoff spilled over into armed clashes between supporters of the rival camps last month and nine people were killed.
It was the country's worst civil unrest since its 1975-1990 civil war and raised fears of a new conflict.
Gemayel meeting
In other news, Amin Gemayel, a former president of Lebanon, met the US president in Washington on Thursday.
"We'll be demonstrating US commitment to a sovereign and democratic Lebanon, and express sympathy, again, on behalf of the president and the American people for the assassination of Mr Gemayel's son, Pierre Gemayel," Tony Snow, the White House press secretary, said.
Amin Gemayel said in an interview broadcast on Sunday that he did not know who was responsible for the killing of his son, the country's industry minister, who was assassinated in November.
But he accused Syria of plotting a coup d'etat against the government of Fouad Siniora, the Lebanese prime minister.