The arrested figures comprise economics professor Nasser bin Ghaith, Fahad Salem al-Shehhi and Ahmed Mansour.
Mansour was arrested on Friday in Dubai after he signed a petition calling for an elected parliament. In early March, a group of Emirati activists petitioned the president of the UAE, Sheikh Khalifa bin Zayed bin Sultan Al Nahyan, to introduce sweeping reforms, including direct elections and a parliament with genuine legislative and regulatory powers.
Based in Abu Dhabi, the UAE comprises seven sheikdoms each run by a ruling family. Its 40-member parliament are appointed by the respective ruling sheikhs or by citizens picked by those rulers.
The seven states are Abu Dhabi, Ajman, Dubai, Fujairah, Ras al-Khaimah, Sharjah and Umm al-Quwain.
The Emirates permit no political parties nor opposition.