The London-based rights group said in a statement that the Al Khalifa regime should explain the charges against Hussain Jawad, the chairman of the European-Bahraini Organization for Human Rights, who was arrested at around 1:30 am local time on Monday (2230 GMT Sunday), press tv reported.
The report said masked men dressed in plain clothes transported Jawad to the Criminal Investigations Directorate, without explaining why they were detaining him.
"Around 10 hours after his arrest, he phoned his wife and said that he was fine. She asked him whether the police had hurt him: he said ‘yes’ and the line was cut off," the statement added.
Bahraini authorities have been asked to give Jawad access to his lawyer, family and any medical attention he may require.
In 2013, Jawad was arrested at a police station South of the capital, Manama, while lodging a complaint. Authorities accused him of "inciting hatred against the regime" in a speech he gave earlier.
Many prisoners taken under custody in Bahrain have reported being tortured or otherwise ill-treated.
This is while Amnesty International has called on Bahraini officials to observe citizens’ rights to freedom of expression and assembly.
Since mid-February 2011, thousands of anti-regime protesters have held numerous demonstrations on the streets of Bahrain, calling for the Al Khalifa family to relinquish power.
Bahraini authorities have since arrested a number of opposition figures and activists, including al-Wefaq National Islamic Society Secretary General Sheikh Ali Salman and prominent Bahraini Human Rights Activist Nabeel Rajab.
Scores of Bahrainis have been killed and hundreds of others injured and arrested in the ongoing crackdown on peaceful demonstrations.