Aljazeera's correspondent in the capital, Manama, quoted the assistant legal undersecretary in the Interior Ministry saying all those detained for protesting in a prohibited zone had been released.
Eyewitnesses said a number of women were among a group of unemployed people beaten and detained for staging a sit-in near the royal court.
Earlier in the day, rights activists said police arrested more than 30 people as they demanded jobs. The government put the number of those arrested at just four.
Activist Nabeel Rajab said Abdulhadi al-Khawaja, head of the banned Bahrain Centre for Human Rights, was among those arrested.
Last year, al-Khawaja was pardoned by Bahrain's King Hamad bin Isa al-Khalifa after being sentenced to a year in prison for publicly blaming the prime minister for the country's economic woes.
Al-Khawaja's detention had led to demonstrations last year in which police clashed with and arrested protesters.
Bahrain is the least wealthy of the oil producing Gulf states, with high unemployment and a history of political tension.
The government says unemployment in the Gulf's banking hub is about 15%, but economists put it at closer to 20%.