"According to information from the Spanish police, he is suspected of extortion for terrorist purposes," said Catarina Axelsson at the Foreign Ministry's press service.
The Swede and five others were arrested in Spain on Tuesday in a series of coordinated raids which also saw 16 arrested in France.
Those detained are all suspected of belonging to the terrorist-classified Kurdish separatist movement PKK. They are suspected of having coerced other Kurds into paying a so-called "revolution tax".
According to the charges, the collections are intended to have been used to finance the purchase of explosives and weapons for terrorist activities in Turkey.
In the course of the raids, police seized weapons and cash.
According to news agency Europa Press the Madrid court released three of the six arrested in Spain, although they remain under suspicion and are not permitted to leave the country.
The 65-year-old Swede, who is reported to be resident in the south of Sweden, is receiving assistance from the embassy and the Swedish Ministry of Foreign Affairs.
The PPK is a Kurdish organization founded in 1984 that fights against the Turkish state for an autonomous Kurdistan, as well as for the rights of Kurds in Turkey.