Aged 38 and 33 and identified by their first names Amir and Nasimeh, they were said to have been planning a bomb attack on Saturday at a conference organized by the NCRI in a Paris suburb.
Citing the joint Belgian statement, the council said that the couple, who pretended to be supporters of the People's Mujahedin organization of Iran, were found carrying 500 grams of materials used to make high explosive triacetone triperoxide (TATP), and a detonator mechanism in a woman's makeup bag.
In a meeting with the French ambassador and the German chargé d'affaires, Iranian Deputy Foreign Minister for Political Affairs Abbas Araqchi expressed Tehran's strong protest over the detention of the Iranian diplomat.
The pair, who are both Belgian nationals of Iranian origin, have been charged with attempted terrorist murder and preparation of a terrorist act.
Austria also informed Iran on Tuesday that the diplomat would be "deprived of his diplomatic status within 48 hours because of the existence of a European arrest warrant" against him, said the spokesman, Matthias Forenbacher.
Three other arrests were made in France but two of them were later released.
NCRI is an umbrella bloc of opposition groups in exile that seek an end to Shia Muslim clerical rule in Iran.
The mullahs stole the 1979 Islamic revolution from the people of Iran and ever since the NCRI have been fighting to bring another revolution, which will put the people in power.
Not a week goes by without our reading in the news that Iran is involved, directly or indirectly, in a terrorist plot, not only in its area of influence but also in far away countries. "Freedom is right around the corner ..."
Trump's recent appointment of John Bolton, who spoke at a MEK rally before he became national security adviser, and Giuliani, a regular MEK headliner, are seen as moves that could strengthen the group's bid for US backing.