"The Swedish policy is not to pay ransom in connection with kidnappings", Wallstrom said, referring to her government's general guideline, but refused to take questions on Gustafsson's case.
Sweden's former Foreign Minister Carl Bildt said that Mr Gustafsson's kidnapping weighed heavily on his mind during his time in the role, which ended in 2014.
"I have already spoken to Johan and he was in good spirits and overwhelmed by everything that's going on", Wallström told Swedish radio, saying she would hold a press conference later in the evening.
While the details of the Swede's release are not immediately clear, Wallström added that his release was thanks to "extensive efforts" by the Swedish foreign ministry, police and "foreign authorities".
The bitter story of Johan started in Timbuktu, northern Mali, in November 2011, was abducted along with South African national Stephen McGowan and Dutchman Sjaak Rijke.
He, Rijke and McGown were seized along with several others by a group of armed men while on the terrace of their hotel. It was among several jihadist groups that took control of Mali's north in 2012 before being ousted by a French-led military operation launched in January 2013.
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Johan Gustafsson, kidnapped in Timbuktu in 2011 by AQ affiliate, in on his way home to Sweden.
"We have no information..."
Rijke escaped the extremists when he was freed by French special forces by chance in April 2015 while the current status of McGowan has not been revealed. "I don't think Stephen has been released", said Imtiaz Sooliman, head of Gift of the Givers.
The charity said in May 2017 that it was giving up its negotiating efforts after hitting a "dead end".
He is, however, the last of the three to be freed after negotiations between the Swedish government and AQIM.
The released person was identified as Johan Gustafsson.