In a Twitter post, Jameel Kazem had cast doubt on the country’s electoral process.
The opposition figure had been sentenced to prison and a fine on January 13, 2014. He served his jail term at the al-Hawz al-Jaf prison in the capital, Manama.
Bahrain Mirror news website reported that Kazem was received by Ayatollah Sheikh Isa Ahmed Qassim, Bahrain's leading Shiite cleric, after freedom.
The move came as Bahraini opposition leader Sheikh Ali Salman is still in jail in spite of the fact that his detention has sparked nationwide rallies in the Persian Gulf country for months.
In June, a Bahraini court acquitted the secretary general of Bahrain's al-Wefaq National Islamic Society of the charge of trying to overthrow the government, but gave him a four-year sentence for other charges.
