"The Federal Intelligence Agency has succeeded in exposing a suspect Islamist among their employees", Xinhua news agency cited a local media report.
The man has made a partial confession. His goal was to infiltrate the Federal Intelligence Agency and gather information for a bomb attack on the main building in the German city of Cologne.
He had tried to pass on "sensitive information about the Federal Intelligence Agency, which could lead to a threat to the office".
The man, a bank clerk and a father, was hired by the federal constitution as a lateral entry employee in April 2016 in order to observe the Islamic scene in Germany.
He was "inconspicuous" during the application process, training and in his working fields, according to the authority.