Representative Curt Weldon, a Republican from Pennsylvania said on Sunday the group was in Tripoli to "reinforce the positive steps that have been taken" by al-Qadhafi.
Led by Weldon, the bipartisan delegation arrived as US and British experts were preparing to start dismantling Libya's weapons of mass destruction programmes with al-Qadhafi's blessing.
The delegation was expected to meet with al-Qadhafi before departing on Monday for visits to Afghanistan and Iraq.
Their visit comes on the heels of another North American lawmaker's arrival in landmark visits likely to take the US visitors on a tour of a Libyan weapons facility.
Representative Tom Lantos, a California Democrat, arrived on Saturday in the first visit by an elected US official in more than 38 years.
Weldon, a senior member of the House Armed Services Committee, said earlier the delegation also would visit a university, the Libyan legislative body and "probably" a weapons of mass destruction site.
Though Washington remains wary of al-Qadhafi's government, the Libyan leader has sought in recent years to end the international isolation that has surrounded his desert nation of 5 million people.
Tripoli has endured two decades of US economic sanctions, and al-Qadhafi's recent decision to rid his country of weapons of mass destruction could lead to improved economic relations with Washington. Libya could also be removed from a US State Department list of countries who allegedly sponsor terrorism.