"We strongly condemn the repression and restrictions to the legitimate right of activists to express themselves peacefully," said a group of a activists in a statement received by AFP Tuesday.
The activists described the "arrests targeting those who were calling for rational dialogue" as "disappointing."
The statement did not say how many people were arrested but said they were detained after they staged a sit-in at the headquarters of the sultanate's Consultative Council on Thursday to demand the release of protesters held since demonstrations began in February.
On Friday, a spokesman from Oman's security services said the authorities have arrested a number of people for "inciting unrest and sedition" in the capital Muscat and the southern city of Salalah, state-run news agency ONA reported.
On May 8, police arrested 8 several people who broke into public offices and committed acts of "sabotage" in the east of the country, a spokesman said.
"A number of people violently entered public offices and committed acts of sabotage," in the eastern province of Jaalan Bani Bu Ali, said the spokesman quoted by ONA.
Earlier this year, the normally peaceful sultanate was caught up in the protests sweeping the Arab world, with demonstrators taking to the streets on February 27 to call for better living conditions.
A supermarket and government offices were torched in Sohar on February 28.
An unspecified number of detainees already face charges for setting fire to public and private property, resisting the authorities, blocking traffic and humiliating or attacking state employees in the country.
At the beginning of March, Sultan Qaboos announced a cabinet reshuffle and the creation of 50,000 jobs, while demonstrators have insisted their protests were aimed at "corrupt" officials and not at Qaboos, who has ruled for 40 years.
In early April, police released 57 people arrested in a crackdown on protests in the northern industrial city of Sohar.