Faisal Ahmed Abdul-Ahadwas, 27, was believed to be one of the main administrators of a Facebook group that is calling for protests similar to that have swept North Africa and the Middle East.
The Facebook group, which has over 17,000 members, is calling for nationwide protests and reforms, including that governors and members of the upper house of parliament be elected, the release of political prisoners, greater employment, and greater freedoms.
Online activists said they believe Abdul-Ahadwas was killed by state security and that his body was taken by authorities to 'hide evidence of the crime.'
They argued he was killed because of 'his commitment to a better future for his country.'
Although these allegations could not independently verified, the religiously and socially-conservative kingdom has moved in recent days to quell a possible uprising similar to those in nearby Tunisia, Egypt, Libya, Bahrain and Yemen.
Saudi authorities were recently slammed by rights groups, including the US-based Human Rights Watch, for the arrest of Sheikh Tawfiq al-Amir, a Shiite cleric who was calling for a constitutional monarchy and equal rights for minority Shias.
Salih al-Chaslan, spokesman for the National Human Rights Society of Saudi Arabia said, when asked, that he knew nothing of the arrest of the religious leader, nor of the death of the man from Riyadh.