And a Shiite woman, jailed 18 months for taking part in protests last year and listening to revolutionary songs was also set free after spending more than 10 months behind bars, the opposition said.
The court of appeals "released on Monday Naser al-Raas, who suffers from cardiac problems, for health reasons," one week after he turned himself in and appeared in court, his lawyer, Mohsen al-Alawi, told AFP.
Alawi added that the decision could also be "because he will most probably be proved innocent at the next hearing" set for February 16.
On January 26, Canada urged Bahrain to resolve Raas’ case, two days after he lost his right to appeal the verdict for failing to turn up in court on January 24, when 12 other Shiites were acquitted.
Raas was held for a month after the mid-March crackdown on protests, and then sentenced in October to five years in prison with the other 12 for involvement in protests against Bahrain’s Sunni ruling Al-Khalifa dynasty.
He went into hiding after the verdict, according to Amnesty International.
Alawi said his client will not be able to leave Bahrain because authorities confiscated his passport.
Amnesty International had said that Raas "has a heart condition that his Canadian doctor has said is aggravated by imprisonment, bringing a real threat that he could die behind bars."
It also called his imprisonment a "horror story."
Last week Canada’s deputy foreign minister Diane Ablonczy said her government was pushing for the case "to be resolved expeditiously, particularly in view of Mr. Al-Raas’ grave health concerns."
Raas, a 29-year-old Kuwaiti-born engineer from Ottawa, travelled to Bahrain in early March 2011 to visit members of his family, Amnesty said.
He was arrested at the airport as he prepared to leave the country and was imprisoned for a month in Al-Qala prison, where he claims to have been beaten.
Meanwhile, female protester Fadhila Mubarak was released late Monday, a week after the court of cassation upheld her jail sentence, according to the Facebook page of Al-Wefaq opposition association.
It remains unclear if Mubarak was pardoned, rights activist Yusif al-Mahafda said.
Amnesty last week urged Bahraini authorities to release Mubarak, whom the rights watchdog described as a "prisoner of conscience" claiming she was tortured in detention.
She was arrested at a checkpoint on March 20 for playing music calling for the overthrow of the regime of the Al-Khalifa ruling family, and was asked to turn the sound down, Amnesty said.
Mubarak was convicted of taking part in protests at Pearl Square, the focal point of anti-government demonstrations, possessing CDs and leaflets inciting hatred towards the regime and assaulting a policeman by pulling his shirt, the watchdog said.
She received a jubilant welcome late Monday by thousands of opposition supporters waving Bahraini flags while revolutionary songs were played at the a rally organised by the Shiite-led opposition in Al-Muqsha village, according to footage posted on the Al-Wefaq Facebook page.
Al-Wefaq said the rally that began on Saturday will continue for a week, while authorities said the assembly was authorised for two days only.
But the interior ministry on Sunday said the gatherings were "legal" until Wednesday.
