Hannington Kuteesa hit Lerato Sengadi after a row inside the Big Brother house in Johannesburg on Tuesday.
Sengadi’s family is planning a protest to demand his removal.
Activists says the show’s actions may perpetuate the belief that African men have the right to hit women.
TV company M-Net has defended its decision not to remove Kuteesa, from Uganda, saying it is trying to act in the interests of all the housemates.
As his punishment Big Brother ordered him to apologise to South Africa’s Sengadi during one of their recordings.
It has also provided counselling to both contestants.
But Lebo Marishane from Women’s Net told the BBC this was not enough.
“Television is a powerful medium which reaches millions of people. Keeping that contestant on the show perpetuates the dangerous stereotype that men can abuse women and not be punished,” she said.
“As it is, many women in Africa and South Africa do not report abuse because parts of society still believe that women who get abused somehow asked for it – it is really sad.”
Angry viewers have continued to flood the show’s website with messages condemning Kuteesa.
An M-Net spokesman, however said they had also received complaints about Ms Sengadi for insulting Kuteesa during a discussion about malaria before the incident.
This is the fifth version of Big Brother Africa, which began with 14 contestants from different countries.
It is broadcast across the continent on satellite TV, and some terrestrial channels, and is one of the continent’s most popular reality TV programmes.
In some countries, politicians and church leaders have called for previous editions be taken off air, saying it is immoral, pointing in particular to naked shower scenes. BBC