Saudi prominent rights lawyer Waleed Abulkhair said on Wednesday a court has sentenced him to three months in prison over a petition he signed two years ago criticising the authorities.
Abulkhair told AFP he would remain out of jail pending an appeal of the sentence.
The court in the western city of Jeddah handed down the sentence late Tuesday, citing the lawyer's signing of a petition criticising harsh sentences given to 16 Islamists arrested in 2011.
The sentence was criticised by rights group Amnesty International, which described it as "yet another sign of the arbitrary nature of Saudi Arabia’s justice system".
Hassiba Hadj Sahraoui, Amnesty's MENA programme deputy director, said the trial also illustrated how the authorities "abuse the justice system to silence peaceful dissent in Saudi Arabia".
"This conviction and prison sentence should be quashed. And the pending charges should be dropped," said Sahraoui.
Authorities earlier this month briefly held Abulkhair for setting up an "unauthorised" gathering hall where he held meetings with reformists in the absolute monarchy. He was later freed on bail.
The lawyer is already facing trials in cases linked to his activism.
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In June 2012, he was accused of "disrespecting the judiciary system... contacting foreign organisations and signing a petition demanding the release of detainees," some of whom were being held over suspected terror links, his wife Samar Badawi said at the time.
Three months earlier, the authorities had banned him from travelling to the United States where he had been due to attend a forum organised by the State Department.
And in February 2011, he signed two other petitions demanding political reform in the ultra-conservative kingdom, where political parties are banned.
Abulkhair has created a group on Facebook -- Monitor of Human Rights in Saudi -- which has nearly 7,000 members.
Meanwhile, the authorities on Sunday arrested a Saudi columnist, Tariq al-Mubarak, after he wrote an article supporting the right of women to drive in the only country in the world that bans female motorists, activists said.
In his article in the Asharq al-Awsat daily, Mubarak had criticised what he said were "threats by a small group to use violence to prevent modernity or a small group within the society from demanding their rights."
"They jail people within their extremist thoughts and scare them from living their lives normally," wrote Mubarak.
Saudi authorities had warned women of legal measures if they defy a long-standing driving ban in the ultra-conservative kingdom.
At least 16 women were stopped by police on Saturday and were fined and forced along with their male guardians to pledge to obey the kingdom's laws.