Activists say Zainab al-Khawaja was held along with dozens of protesters demanding political reforms in Gulf kingdom.
Forty people, including the daughter of a leading opposition activist, have been arrested hours after security forces used tear gas and birdshot to disperse hundreds of protesters demanding political reforms in Bahrain, activists said.
Activist Zainab al-Khawaja was arrested early on Friday in a crackdown that left at least 45 people injured, said Mohammed al-Maskati, the head of the Bahrain Youth Society for Human Rights.
Al-Maskati said Zainab was trying to hold a solitary protest sit-in at al-Badei street close to the capital Manama when she was arrested.
Zainab is the daughter of Abdulhadi al-Khawaja, a well-known Shia figure in the Gulf Arab island kingdom who ended a more than three-month-long hunger strike in May after drawing attention to the issue of imprisoned activists.
Bahrain crushed an uprising led by majority Shia Muslims last year, after successful popular revolts in Tunisia and Egypt, but protest marches and rallies continue, leading at times to clashes between police and Shia youths.
Bahraini Shia say they have long been marginalised in political and economic life, which the government denies.
Bahrain's Sunni rulers have rejected the main opposition demand - an elected parliament with full powers to pass laws and form governments.
"She had taken part in the protests and then headed to that street to start a sit-in. That is when she was arrested," Maskati told the Reuters news agency by telephone.
"From the information we have managed to gather from lawyers and the families of protesters, at least 40 others have been arrested as well," he said.
"All three protests were heavily crushed as tear gas and birdshot was used with reports of at least 40 to 45 people being injured," Maskati said, adding that injuries ranged from slight to serious.
Government officials were not immediately available for comment.
The interior ministry said in a statement on its website that "riot instigators" threw Molotov cocktails at a ministry bus in a road near Bani Jamra, but that its driver and his companion escaped uninjured.
Zainab was previously arrested on April 21 for trying to stage a protest in Manama during Bahrain's Formula One Grand Prix.
She was sentenced in May to one month in jail and fined $530 on a separate charge relating to insulting a government employee.
"I still haven't managed to find out exactly what the charges pressed against her are," her lawyer Mohammed al-Jishi said.