South Africans Nick Du Toit, with Sergio Cardoso, Jose Sundays and George Alerson, along with British citizen Simon Mann, had been sentenced to 34 years in prison but were granted presidential pardons on humanitarian grounds.
They had been jailed for their role in a 2004 plot to oust President Teodoro Obiang Nguema as head of the former Spanish colony.
South Africa banned all mercenary activity in 1998, and tightened the law after the coup attempt in Equatorial Guinea.
However Tlali said if new allegations against the four were to emerge, new charges will be investigated.
“If it appears that there are other allegations they were never tried for, these allegations will receive attention of the law agencies,” he said.
Mann returned to Britain yesterday, but the four South Africans have yet to return home. The foreign ministry said it could not provide any details on their travels.