The investigation into purported links between Salman and Qatar was first launched in August, after a quartet of Arab countries.
The investigation into purported links between Salman and Qatar was first launched in August, after a quartet of Arab countries -- Bahrain included -- accused their gas-rich neighbour of supporting terrorism and close relations with Shiite Iran.
State-run Bahrain Television aired a report which claimed that neighbouring Qatar was behind anti-government protests that have shaken the tiny kingdom for the past six years.
It alleged that Qatar's former premier Sheikh Hamad bin Jassem Al-Thani contacted Salman -- then head of Bahrain's largest opposition group, Al-Wefaq -- in 2011 and asked him to urge protesters to flood the streets and ramp up pressure on the state.
Salman has been behind bars since 2014 serving a nine-year sentence for allegedly inciting hatred.
He has now been charged with "spying on behalf of a foreign country ... with the aim of carrying out subversive acts against Bahrain and harming its national interests," the Bahraini prosecutor's office said in a statement.
The dissident was also charged with "revealing defence secrets to a foreign country and disseminating information that would harm Bahrain's status and reputation".
The statement did not say when the trial would begin.
Al-Wefaq was the largest group in parliament before its lawmakers resigned en masse in protest at the crushing of Arab Spring-inspired demonstrations in 2011 calling for an elected government.
The Shiite Muslim movement has called for Sunni-ruled Bahrain to become a constitutional monarchy.
The Shiite majority in Bahrain, which has been ruled by the Al-Khalifa dynasty for more than two centuries, has long complained of marginalisation and the country has been rocked by sporadic unrest since 2011.