A US citizen was detained in northern Iran, a court spokesman confirmed on Monday, according to news agency ISNA.
The charges facing the man are still unclear, said Gholamhussein Mohseni Edzehi, court spokesman in the city of Gorgan.
His case is set to be transferred to the capital city Tehran, Edzehi added.
The man is thought to be Robin Shahini, an Iranian-American man, who sharply criticized Iran's human rights violations on social networks after visiting family in July.
His sister reported him missing earlier this month and suspected he was arrested for his comments, ISNA said.
In recent months, four Iranians with dual citizenship - two Americans, a Canadian and a Britain - have been arrested and accused of collaborating with Western intelligence agencies with the goal of bringing down the Iranian government.
Because those arrested are part Iranian, they are treated as such - meaning no legal counsel from relevant consulates. If found guilty of espionage, they face the death penalty or long prison sentences. If the charges cannot be proved, the suspects will likely be released and forced to leave the country.