Human rights groups both inside Iran and abroad have condemned the arrest of one of the country's most outspoken and high profile human rights activists.
Mr Baghi is one of Iran's most prominent human rights activists
Journalist Emadeddin Baghi was arrested on Sunday when he responded to a court summons and has been denied bail.
The watchdog Reporters Without Borders has called for his release.
The state-run Iranian news agency quoted an official saying Mr Baghi's family had taken part in meetings to discuss toppling the government.
The imprisonment of Mr Baghi has raised fears that the Iranian government has decided to take a tougher line with its critics to silence them.
Mr Baghi has been a tireless campaigner for human rights in Iran despite having his passport confiscated, his newspaper closed, suspended prison sentences passed against his wife and daughter and being jailed himself.
He runs the Association for Defending the Rights of Prisoners which monitors allegations of torture and works for the abolition of the death penalty in Iran.
Reports say an earlier suspended sentence against Mr Baghi was converted into imprisonment which meant he could be denied bail.
He has also now been accused of publishing secret government documents obtained with the help of prisoners on security charges.
Students have been at the forefront of anti-government protests in Iran
His family have no idea where he is being held but fear he is in solitary confinement, which is routine in political cases.
Reporters Without Borders have issued a statement urging all democratic countries firmly to condemn the arrest and calling for the release of all Iranian prisoners of conscience, whom it says are increasing in number by the month.
Reformist students in Iran, whose colleagues have also been jailed in recent months, have come out in support of Mr Baghi, calling him one of the very few active defenders of human rights there.
Some observers worry this latest incident means the Iranian government is changing its approach towards prominent human rights activists and instead of harassing and intimidating them intends to put them behind bars.