He jumped into the bottom tier of the Trent End to celebrate, and when he emerged he was shown his second yellow card of the match.
The goal was little more than Forest deserved as they recorded a fifth straight league win for the first time since April 2005.
The closest Barnsley went to scoring was in the second minute after Wes Morgan fouled Jon Macken 25 yards out.
Iain Hume curled the free-kick over the wall and beyond Lee Camp but the ball clipped the top of the crossbar.
The Yorkshire side came again after seven minutes and good link-up play between Hume and Macken created a shooting chance for the Canadian but he volleyed wide.
Forest began to get their passing game going but it was all in front of the Barnsley defence and lacked penetration.
That was until Nathan Tyson got free down the left side midway through the first half.
His far-post cross was headed back across goal by Dexter Blackstock. With the goal gaping, David McGoldrick looked certain to score but, at full stretch, he somehow poked the ball up and against the face of the crossbar from two yards out.
Undeterred, the summer signing from Southampton tried to make amends and a minute later timed a run perfectly to beat the offside trap but saw his powerful shot blocked by Luke Steele's legs.
McGoldrick spurned a third opportunity in the 35th minute following another Tyson cross.
Instead of striking the ball first time he tried to control it and was closed down by Barnsley defenders. Paul McKenna's shot from the rebound cleared the crossbar.
Barnsley reminded their hosts they were still in the game when Macken forced Camp to get down quickly to his right to smother a low shot from the edge of the box in first-half stoppage-time.
But there was still time for Forest to twice go close at the other end.
First Steele blocked Blackstock's driven shot from 10 yards before Anderson curled an effort through a crowded penalty box just wide of the far post.
Forest resumed after the break in the same manner and after Blackstock had volleyed over, Tyson rolled a shot just wide after timing his run behind the Barnsley backline.
A rare spell of pressure from Barnsley just after the hour mark saw Camp push a well-struck Adam Hammill effort round his near post before Tykes captain Stephen Foster glanced a header narrowly wide following some poor marking from Forest.
Substitute Julian Gray then headed into the side-netting.
At the opposite end, Foster was relieved to see his defensive header miss the top corner of his own net midway through the second half.
Barnsley were buoyed by their spell of pressure and Camp had to palm away another shot in the 80th minute, this time from Emil Hallfredsson.
It looked like both sides were going to extend their unbeaten runs - Barnsley arrived in the East Midlands on the back of a three-game winning streak of their own - but Moussi struck in the third minute of stoppage-time.
His elation soon turned to disbelief, however, after he was dismissed.