Venter will be available for Warriors' URC play-off fixtures and the Champions Cup semi-final, should they overcome Leinster.
"Venter accepted he had committed an act of foul play, and that it would have warranted a red card, but that it was not intentional," European Professional Club Rugby said.
"It was decided that the offending was at the mid-range of World Rugby's sanctions and 12 weeks was selected as the appropriate entry point."
The independent disciplinary committee took into account "the player's timely acceptance that he had committed an act of foul play that would have warranted a red card, his expression of remorse, clean disciplinary record and good conduct and full participation in the disciplinary hearing".
It therefore "decided to reduce the sanction by the maximum of 50% before imposing a six-week suspension".