Mustafa Sanalla, a boad member of the company, said operations at Sharara, closed by protests in October, resumed during the weekend, the Platts energy news service reported.
Protesters who forced the shutdown had demanded more local authority, officials said.
"Today production is 205,000 bpd from Sharara," Sanalla said.
The field in western Libya has the capacity to produce 350,000 bpd.
Libya has struggled to return to its pre-civil war level of 1.6 million bpd because of national security issues.
Platts reports there were no indications crude oil from Sharara has reached the export market.
In 2012, the International Energy Agency called on its member states to tap into their strategic reserves to compensate for supply disruptions in Libya.
Production increases from North America provided the global oil market with a buffer against Libyan supply issues.