Saudi Arabia is attempting to silence the country's leading human rights organisation, according to Amnesty International.
Eleven members of the Saudi Civil and Political Rights Association (ACPRA) have been jailed or are on trial.
Amnesty alleges that some were ill-treated for speaking out against human rights violations in the country.
They were arrested under a new anti-terror law in force since February. Other activists have also been jailed.
Members of ACPRA, an independent human rights group founded in 2009, have been charged with "breaking allegiance to and disobeying the ruler" and "inciting public opinion against the authorities", according to Amnesty.
Of the 11, three are serving prison sentences of between 10 and 15 years, three are facing re-trials, two are on trial, two have been detained without trial and one is now free pending an appeal.
Amnesty claims that some of the men were subject to ill treatment. Saleh al-Ashwan, 30, who is being detained without trial was allegedly stripped, beaten and hung by his limbs from a ceiling.
Said Boumedouha, Amnesty International Middle East and North Africa deputy director, said: "The convictions of all ACPRA activists in detention should be quashed and they must be released immediately and unconditionally."
Saudi Arabia has been criticised previously by international human rights groups who claim the country treats its citizens unfairly.