The Swedish domestic security agency said a person has been arrested on suspicion of having been recruited by Russia to carry out "illegal intelligence activities against Sweden".
Daniel Stenling, head of the SAPO's counter espionage unit, said the individual "works in the Swedish high-tech industry" and has information that the agency knows is of interest to foreign intelligence services.
Mr Stenling said that the SAPO has worked on the matter "for a long time" and that the present alleged crime has been going on since at least 2017.
The person was recruited by a Russian intelligence officer who works at Russia's Embassy in Stockholm under a diplomatic cover, he said. The suspect was arrested on Tuesday evening during a meeting in central Stockholm.
No other details are available.
The SVR, Russia's foreign intelligence service, made no comment.