Marzieh Hashemi, 59, arrived in Tehran on Wednesday, according to state-run English-language channel Press TV.
She was held as a material witness and testified in an undisclosed federal investigation, a US federal court order said last week when she was released.
Hashemi, a US citizen, was welcomed by her colleagues in a special ceremony upon her arrival at Imam Khomeini International Airport, according to the report.
Hashemi, who works for the Press TV network’s English-language service, was arrested by federal agents on January 13 in St Louis, Missouri, where she had filmed a Black Lives Matter documentary after visiting relatives in the New Orleans area, her son said.
She was then transported to Washington, DC where she had remained behind bars until January 24.
Hashemi had appeared in court at least twice before a US district judge in Washington, DC and court papers said she would be released immediately after her testimony before a grand jury.
Court documents did not include details on the criminal case in which she was named a witness.
The journalist’s detention came amid heightened tensions between Iran and the US after President Donald Trump withdrew from a nuclear deal. Iran also faces increasing criticism of its own arrests of dual citizens and other people with Western ties.