There are reports of protests by hundreds of people in the Libyan city of Benghazi.
Eyewitnesses told the BBC that the unrest had been triggered by the arrest of a lawyer who is an outspoken critic of the government.
The lawyer was later said to have been released but the protests continued.
Pro-democracy protests have swept through several Arab countries in recent weeks, forcing the leaders of Tunisia and Egypt from power.
A call has been put out on the internet for protests across Libya on Thursday.