Could be. Anticipation of the shot isnt uncommon, even with people who have been shooting a long time. You also want to follow through, and hold that sight picture through the hammer fall, and with a live round, through the cycle, so youre right back to a sight picture when its complete.
One thing you can try if you think your are doing it, is while youre shooting, revert to "dry fire mode" and mentally tell yourself youre dry firing, and all that will happen when the shot breaks, is the hammer will fall in a click and youll be holding the sight picture on target, even after the fall, calling your shot. Concentrate on a perfect sight alignment and stroke or squeeze the trigger. Think of it as psyching yourself out.