Voters are electing candidates for a 200-seat national assembly, which will form a temporary government and draft a constitution, Voice of America reported.
The assembly will choose a cabinet and prime minister, and full parliamentary elections are to be held next year.
The election comes less than nine months after the end of the revolution that led to dictator Moammar Gadhafi's ouster and eventually his death.
The Tripoli Post reported some violence in the eastern part of the country and said an official of the Electoral Commission, Abdullah Al-Barassi, 22, was killed when the helicopter he was in was targeted by small arms fire east of Benghazi. VOA said the motive for the attack remained unclear.
Also in the east, supporters of autonomy called for a boycott of the elections and threatened to sabotage polling. A polling station in Benghazi was attacked by pro-autonomy activists, who seized electoral papers and ballot boxes, and ballot papers were set on fire at an election office in Ajdabiya, the BBC said.
The British broadcaster said many people in eastern Libya worry the area, rich in oil, will be under-represented in the assembly.
Some former rebels had threatened to disrupt the vote by targeting the oil industry.
Former rebels have shut down up to five oil terminals, the BBC said, reducing Libya's ability to export oil.