The occupiers demanded that some of the government ministers be removed because they allegedly have ties to the late Moammar Gadhafi's regime, the BBC reported Thursday
The protesters were believed to be in talks with politicians to resolve the standoff, the British broadcaster said.
At least a dozen trucks outfitted with anti-aircraft guns lined the main road to Parliament.
Libya held a peaceful election in July and reached agreement on the composition of a government Wednesday. Prime Minister Ali Zidan earned support of the National Congress for his slate of ministers, which included liberals and Islamists in an attempt to create a coalition acceptable to all parties.
Negotiations broke down earlier this week and gunmen breached security lines to occupy the government building Wednesday.
"Some of them have had long ties with Gadhaf; we don't want them," one man told the BBC.
Presidential guards were ordered not to fight with the gunmen.