Diagnosis
Spark module is stuck in spark mode for that burner. Moisture or food debris in the electrode area is the most common cause.
How to Fix It
Lift the burner grate and cap off. Clean the entire burner head area. Use a toothbrush and rubbing alcohol on the electrode (the small metal pin next to the burner). Dry thoroughly. Ensure burner cap is seated perfectly flat.
If That Didn't Work
The spark electrode may be cracked or the wire to the spark module may be damaged. Inspect the ceramic insulator on the electrode for cracks.
Heads Up
Continuous sparking can damage the spark module. If cleaning doesn't stop it, unplug the range until repaired to prevent module failure.