Probably just organic waste that collected and burned onto the heater. Unplug it for a few minutes, then take it out. Get a paper towel and wrap around the burned part. Then add some white vinegar to it and let it soak for 30 minutes, then see if it comes off.
No problem, though check to see if you have an appropriate wattage heater for the amount of water in your tank. My heaters usually only tick on for a short time to maintain temps.