HUNTINGTON BEACH, Calif.—An 18-year-old Southern California high school student has been charged with reporting a false bomb threat after police say he left a note on his teacher's desk warning of an explosive.

Orange County prosecutors said Tuesday that Christopher Michael Casey threatened to detonate a bomb at Huntington Beach High School on Dec. 14, the same day as the shooting at a Connecticut elementary school.

The note was found by a secretary, who called police.

Police searched the school and didn't find any weapons or explosives.

Prosecutors are requesting $250,000 bail.

Casey is to make an initial court appearance Tuesday afternoon.