Mohammed Salem al-Zumer was arrested by state security officers in the emirate of Sharjah on Wednesday and taken to an unknown destination, according to the London-based Emirates Center for Human Rights (ECHR).
Al-Zumer had reportedly posted comments on the Internet supporting jailed activists.
Last month, the Persian Gulf littoral state tightened its law on Internet use, making it an offence to deride or damage the state or its institutions and organize protests.
According to the ECHR report, Zumer was driving a car when he was stopped by security personnel, and was escorted to his home, where plainclothes officers searched for more than an hour.
The UAE has launched a crackdown on activists campaigning for free speech and political freedom in the past year and more than 60 activists have been arrested since then.
UAE officials have also revoked the citizenship of several activists who had called for reforms.
Al-Zumer is the son of a well known poet in the Emirates and his mother is the sister of Khaled al-Sheiba al-Nuaimi, who was detained in July.
Rights groups have slammed Abu Dhabi for the ongoing crackdown.
