It's unclear how many will be freed.
Two of those in the case are being tried in absentia, including opposition leader Hassan Meshaima, who has been in self-exile in London since last year. He plans to return from London to join the protesters.
Meanwhile, government supporters are also demonstrating their support for the king.
At least eight people have been slain and hundreds injured in street clashes, which included the army opening fire on protesters in the capital Manama. The attack brought stinging denunciations from Bahrain's Western allies, including the United States. The U.S. maintains very close ties with Bahrain, which hosts the U.S. Navy's 5th Fleet.
Thousands of people gathered in Bahrain's capital on Tuesday to attend a funeral for a man killed during the protests.
On Monday, Bahrain's crown prince called off Formula One's season-opening race scheduled for March 13 because of the demonstrations.
The Associated Press contributed to this report.