The striker, on loan from Port Vale, converted Lee Brown's left-wing cross at the far post to settle a competitive game and maintain his side's climb up the table.
Rovers went in front after seven minutes when Mohamed nodded on a Michael Smith long throw and Chris Beardsley stooped to head in off the far post.
The hosts had chances to increase their lead before Argyle hit back on the stroke of half-time.
Goalkeeper Steve Mildenhall could only block a free-kick and Michael Blanchard headed the loose ball across goal for Neal Trotman to nod home from close range.
Plymouth's goal had led a charmed life two minutes earlier when in a matter of seconds Tom Parkes had a header saved, Ollie Clarke saw two shots blocked, Lee Brown had an effort cleared off the goal-line and David Clarkson blasted into the side-netting.
Mildenhall later produced a brilliant save from substitute Marvin Morgan's header to deny Argyle a second equaliser.