According to Mir’at al-Bahrain website, he was released on Monday.
Mashaal was detained by Al Khalifa regime’s security forces after they raided his home in July 2016.
He had called for rallies in support of Bahrain’s top Shia cleric Sheikh Issa Qassim.
Sheikh Qassim himself has been tried at a court over trumped-up charges and been stripped of his citizenship.
The Islamic Scholars Council was founded in 2004 under the leadership of Sheikh Qassim.
On January 29, 2014, a Bahraini court decided to dissolve the council, which includes a number of prominent Bahraini Shia scholars, and ordered the liquidation of its assets.
Bahrain, a close ally of the US in the Persian Gulf region, has been witnessing almost daily protests against the ruling Al Khalifa dynasty since early 2011, with Manama using heavy-handed measures in an attempt to crush the demonstrations.
Scores of Bahrainis have been killed and hundreds of others injured and arrested in the ongoing crackdown on the peaceful demonstrations.