The dissident group the protesters were linked to told Aljazeera.net on Tuesday the relatively mild sentences passed down by the traditionally strict Saudi authorities came as some surprise.
"A summary court on Sunday sentenced 36 Saudi men and women to 55 days in prison for taking part in a gathering in the al-Ulaya area two months ago," the English-language Arab News said on Tuesday.
"The judge ordered the group to be released for time already served after it was confirmed they had fallen prey to a dubious party calling itself the Movement for Islamic Reform," it added.
MIRA has called for and organised several demonstrations in Saudi Arabia, with several hundred people taking to the streets on 14 October calling for reforms.
The protests, held during the first human rights conference to be held in the kingdom, led to the arrest of 271 people.
Speaking from his exile in London, Dr Saad al-Fakih told Aljazeera.net that MIRA had been expecting harsher punishments to be meted out to its supporters.
Al-Fakih did not know why lighter sentences had been delivered but speculated that rivalry between Saudi princes, flourishing in the political void created by King Fahd's failing health, may have led to an intervention by a member of the royal family.
He said the cases showed the Saudi royal family could not crush peaceful opposition and MIRA supporters would be encouraged to take part in further protests, which the dissident group planned to call for again in the coming weeks.
The London-based MIRA urges major reforms in Saudi Arabia, namely freedom of expression and assembly as well as the abolition of the secret police as a precondition for political, judicial, economic and social reforms in accordance with Islamist principles.