The Security Police said in a statement they had searched five locations in connection with the case and told the press that it had detained a resident of Latvia under Article 85 of the country's Criminal Law concerning espionage.
That specifies the illegality of "collection and transfer to a foreign country or foreign organization directly or via an intermediary of classified information."
It was not disclosed if the person had been in contact with or had been acting under orders from foreign intelligence services.
As the investigation is ongoing, the Security Police abstained from further comment.
Nevertheless, it marks a notable development as until now it was not clear whether it was even policy to tell the public when and if espionage suspects had been apprehended.
That is in contrast to the practice in Estonia and Lithuania which have gone public in such cases.
If proven, the crime is punishable by up to ten years in prison.