The incident occurred during Leicester's 25-21 victory at Welford Road on December 7.
The game has since become notorious for Toulon prop Martin Castrogiovanni's expletive-filled rant against against Leicester director of rugby Richard Cockerill, which earned the Italian a €10,000 fine and a suspended four-game ban.
On Wednesday, EPRC released a statement confirming that Armitage, who pleaded not guilty, had been banned for 12 weeks for using foul and abusive language towards Leicester fans.
"The misconduct complaint against Armitage was that during and after the match he was alleged to have conducted himself in an unsportsmanlike manner by making a number of comments to, or within earshot of, spectators using foul and abusive language and may have brought into disrepute the sport of rugby union, the European Rugby Champions Cup, other clubs and persons and/or EPCR in contravention of the Disciplinary Rules of the European Rugby Champions Cup Participation Agreement 2014/15," the statement read.
The governing body decided that it: "was satisfied that Armitage had directed abusive language at Leicester Tigers supporters after the match, and while it found that his comments were provoked, the committee decided he was guilty of misconduct."
The usual sanction for such an offence would be eight weeks but, as it is Armitage's second breach in the previous four years, after he pushed an anti-doping officer following a match for London Irish in January 2011.
Armitage's suspension will run through until March 8 2015.