Cricket South Africa (CSA) made the announcement without detailing whether any matches were under investigation, or saying who the individual is.
It said its Anti-Corruption and Security Unit had also charged the individual with failing to co-operate.
The Ram Slam T20 Challenge was won on Saturday by the Titans franchise.
The Pretoria-based Titans beat the Durban-based Dolphins by seven wickets, with former England batsman Kevin Pietersen on the losing side.
CSA said the intermediary had been charged with "contriving to fix, or otherwise improperly influence aspects" of the series.
It added the individual has been "provisionally suspended" from any involvement in competition "recognised or supported in any way by CSA, the International Cricket Council, a national cricket federation or any member of a national cricket federation".
South African cricket authorities have charged an unnamed "intermediary" with attempting to fix matches in a domestic Twenty20 competition.