An appeals court is reviewing that conviction, but the prosecution is demanding the annulment of his acquittal on the more serious charge of plotting to overthrow the regime and seeking a tougher sentence.
A ruling on the appeal is expected on March 30.
Al-Wefaq renewed earlier calls for its leader to be released “immediately”.
The group once held the most seats in parliament, but its 18 MPs walked out in 2011 in protest at violence against demonstrators during pro-democracy rallies.
Bahrain’s authorities crushed Shia-led protests a month after they erupted on February 14, 2011.
The gap has since been growing between the Sunni authorities and their mainly Shia opponents.
Tiny but strategic Bahrain across the Gulf from Shia Iran is home to the US Fifth Fleet, and on October 31, construction work also began on Britain’s first permanent military base in the Middle East since 1971.