Mahama has condemned Thursday’s violence at La Bawaleshie during the Ayawaso West Wuogon by-election.
Men dressed in black polo shirts and khaki trousers stormed a polling station where voting was ongoing to elect a new MP.
The men are alleged to have fired gunshot and even slapped Ningo-Prampram MP Samuel George, who in a video, appeared to be questioning them.
The NDC reacted to the violence by withdrawing from the by-election, accusing the NPP and the president of deliberately intimidating voters and their polling agents.
Police in a statement put the number of injured persons to six and dispelled rumours that there were fatalities.
They say the injured are responding to treatment at Legon and 37 Military hospitals.
But Mahama, who blames the NPP for the violence said the NDC can do worse, warning the governing NPP that the opposition party will meet boot for boot in 2020.
John Mahama made the comments in the Volta Region on Thursday as part of a campaign tour ahead of NDC presidential primaries on February 23.