The suspect has been under surveillance for some time and was arrested by the security police in the capital on Thursday, Säpo said in a statement.
Säpo added that it was bound by confidentiality agreements and was not at liberty to divulge any further details about the case.
A public prosecutor has until lunchtime on Sunday to decide whether the suspect should be remanded in custody.
“These cases are difficult to detect and difficult to investigate. First of all, there’s never anybody who reports a crime,” prosecutor Tomas Lindstrand told news agency TT.
“The crime is predicated on the involvement of a foreign power and mostly, though not always, the people in charge are very good at what they do. They take every possible precaution and I think I’d go as far as to say that they are considerably more careful than many people involved in more traditional serious crime.”
The crime of ‘refugee espionage’ (flyktingspionage) is widespread in Sweden, according to Säpo, with a number of countries committing major resources to gathering information about dissidents who have fled their domestic borders for Sweden.
The crime is considered serious and is viewed as a threat to Sweden’s national security.
In 2008, Säpo revealed that an intelligence officer stationed at an undisclosed embassy had been declared persona non grata and deported from Sweden after he was found to have spied on refugees and threatened them with torture and imprisonment if they refused to assist him with his covert operations.
Säpo said its investigations in the case had also led to the deportation of several intelligence agents who had cooperated with the undercover officer.