Iranian authorities said two German nationals posed as reporters when they interviewed the son of Sakineh Mohammadi Ashtiani.
Originally sentenced to death by stoning, Ashtiani was convicted in 2006 of having an affair with two men after the death of her husband. She confessed on state-run television in August to adultery and murder but her lawyers said the confession was coerced.
Her execution was suspended in July amid an international furor over Iran's human rights record.
Tehran said the two Germans confessed to breaking Iranian laws. According to Iran's state-funded broadcaster Press TV, a person close to the family reported the Germans to authorities because of "suspicious behavior."
Iranian President Mahmoud Ahmadinejad complained during the summer that Western allies were biased on the Ashtiani case, noting more than 50 women were on death row in the United States.
Iran is at odds with the West over its human rights record. Iranian lawmakers are expected to vote on a measure this week to cut ties with London over controversial remarks by the British ambassador to Tehran.