Just days before Bahrain's most prestigious international sporting event, the Formula One Grand Prix, security forces have used stun grenades to disperse anti-government protesters at an exhibition about the race.
Last year's race was cancelled after at least 35 people were killed during a crackdown on pro-democracy protests.
A local journalist says the demonstrators in Old Manama were shouting "Down, down, F1" and demanding the release of Abdulhadi al-Khawaja, the activist who has been on hunger strike in prison for more than two months.
Mr Khawaja's lawyer earlier told the BBC his client had removed the intravenous drip keeping him alive and had told his wife he was also now refusing anything but water.
Mr Khawaja was convicted by a military court in June of plotting against the state, but human rights groups have said that his trial was "grossly unfair" and his conviction was based on a confession he made under duress.
Bahrain's highest court is due to rule on Mr Khawaja's appeal against his conviction on Monday - a day after the grand prix.
Activists allegedly rounded up
Formula 1's governing body, the FIA, only decided to go ahead with this weekend's race at the last minute.
The protesters are determined to use the race to draw world attention to their year-long campaign for democracy, and to the government's continuing suppression.
The government, run by the ruling Al Khalifa family, is determined to stop them. Opposition groups say between 60 and 80 activists have been taken from their homes in the past few days as the government rounds up those it fears will cause most trouble.