Five of the defendants were ordered to surrender Saturday to begin their jail terms, Gulf News reported. The three judges ruled a medical student can complete the semester before he goes to prison.
A lawyer said the six, who were also convicted of violating Oman's laws on use of the Internet, are running out of options.
"They will appeal to the Supreme Court but their prison term stays even after the appeal," Sami al-Sa'adi told Gulf News.
Forty-two activists have been put on trial. The arrests began in May when three men were detained for protesting on behalf of striking oil workers.
Some defendants have been charged both with cyber crimes and street protests.
The Sultanate of Oman, with a population of about 2.7 million, is in the southeast corner of the Arabian Peninsula.