"It's time the ruling families took the initiative... and transformed into European-style monarchies," said a statement signed by the liberal Gulf Civil Society Forum coordinator, Anwar al-Rasheed.
This will respond to the Gulf peoples' continued "demands for reforms, fighting corruption and becoming democratic states like other countries of the world," the statement said.
All six states of the Gulf Cooperation Council are ruled by monarchies which enjoy almost absolute powers, controlling all key government positions and with rulers having the final say in internal and external affairs.
The bloc, which groups Bahrain, Kuwait, Qatar, Oman, United Arab Emirates and Saudi Arabia, sits on around 45 percent of global oil reserves and 30 percent of natural gas deposits. Together they pump just under a fifth of world crude.
Only Kuwait and Bahrain have elected parliaments but their powers are limited. The Saudi Shura (Consulative) Council is appointed by the king.
Bahrainis have been demonstrating for the past week demanding sweeping reforms.
Corruption has been on the rise in line with the sharp increase in oil wealth.
The Gulf Civil Society Forum is made up of liberal intellectuals, academics and human rights activists from the six states.