A Bahraini human rights activist who was arrested for spreading false news on Twitter has been acquitted.

Yousif al-Muhafda of the Bahrain Centre for Human Rights (BHCR) was found not guilty of "posting inaccurate news about anti-government protests" on the popular microblogging site.

He was previously released on bail in January after being detained at a pro-democracy rally in Manama in December. "The court acquitted me today, but I had spent a month in jail," Muhafda said.

"We call on the Bahraini government to stop targeting human rights activists and release the head of the centre, Nabeel Rajab."

Muhafda posted tweets describing a shotgun injury, teargas and "security forces spraying pepper spray on female protesters' faces as they mock them/laugh" during a pro-democracy rally in Manama.

Prosecutors argued that a picture, posted on Twitter and showing an injured leg, caused protests and acts of sabotage that "disrupted security on that same day", according to the Bahrain's government news agency.

Human rights activists had claimed the arrest was part of a growing clampdown on social media posts.

"The authorities are placing extensive surveillance on social media, and several were arrested because of their online posts in an act that serves to intimidate others to move into self-censorship," the Gulf Centre for Human Rights and the BCHR said in a joint statement.

In October, four men were arrested in Bahrain for "misuse of social media" and charged with defaming king Hamad bin Isa al-Khalifa on Twitter.

Criticising King Hamad and other members of the Khalifa ruling family is forbidden in the tiny Gulf kingdom.

Earlier this month, prominent human rights activist Zainab al-Khawaja was sentenced to three months in prison for "insulting and humiliating a public employee".

She had previously served sentences of one and two months on separate charges. Her father, Abdulhadi al-Khawaja, was among eight activists sentenced to life in prison for their opposition to the Khalifa regime.

The UN Human Rights Council issued a statement criticising "the continued harassment and imprisonment of persons exercising their rights to freedom of opinion and expression in Bahrain".