Supporters said on Tuesday, that university professor Tawfiq al-Qusayyir and lawyer Sulaiman al-Rushdi were freed on Monday. They did not say whether any conditions had been set for their release.
"They were released yesterday. We are hoping that two more may be freed today," said one activist.
Also on Tuesday, prominent Saudi liberal lawyer Muhammad Said Tayyib was released after two weeks in detention, his wife told AFP from the Red Sea city of Jidda.
Tayyib was not immediately available for comment. His release came one day after the other reformists were freed after 13 days in detention, saying they had not pledged to cease their pro-reform activities.
The men were among a group of 13 activists rounded up earlier this month after signing petitions calling for a constitutional monarchy and urging the royal family to set a timetable for political change. Three are still detained.
Saudi Arabia, the world's biggest oil exporter and birthplace of Islam, has launched a programme of cautious reforms including municipal elections later this year.
De facto ruler Crown Prince Abd Allah has promised the reform process is unstoppable, but also warned the kingdom would not be embarking on "reckless adventures".