"They were released yesterday. They arrived in Sweden today at midday,"
press officer Cecilia Julin told AFP on Saturday.
The three were helped in their return by the Swedish embassy in Addis Abeba. They will be reunited with their families on Saturday afternoon.
The three Swedish citizens were taken prisoner at the beginning of the year. A fourth prisoner, a pregnant 17-year-old, was released in March.
The group were arrested in Kenya, having fled Somalia after the invasion by Ethiopian troops which brought about an Islamist retreat. Around 60 others were also arrested and sent to Ethiopia via Somalia.
The prisoners were accused of fighting on the side of the Islamist militia against Somali government forces and their Ethiopian allies.
Human rights organizations criticized Ethiopia for holding the prisoners in contravention of international law.
Earlier in the month, Sweden had demanded the immediate release of the three. The foreign ministry summoned Ethiopia's ambassador in order to hand over a formal protest.
At first Ethiopia rejected the demands, saying that "the suspects of terror, whatever their nationality, should be brought to the court of justice".
Sweden's foreign ministry has not been given an explanation for the about-turn, and nor is it clear if the suspicions against the Swedes remain.
"I have no information about the details of the release. All along, we've demanded that they [the Ethiopian authorities] either give us an explanation of the legal grounds for the arrests or let them go free," said Cecilia Julin.