A 17-year-old Long Island boy was arrested yesterday for allegedly scrawling a terrorist threat against a Levittown high school on park bleachers.

Anthony Larosa, of Levittown, was accused of writing at the Town of Hempstead Park, “I am going to shoot up McArthur on Friday 10/15/10” and, “This is not a joke.”

It was not immediately known if Larosa was a student at the school or whether he had retained an attorney.