Johnson, 33, was arrested after being detained by a school resource officer. Shenandoah County Sheriff's Office Major Scott Proctor told CBS affiliate WTVR that Johnson was approached by a school employee immediately after he entered the school. He said the school resource officer arrived "seconds later."
Proctor said he was not sure why Johnson entered the school, however he said it appeared Johnson wanted to make a point about school security.
Proctor was not aware if Johnson had a child at the school, which shares the same name as the school in Newtown, Conn. where a gunman opened fire last week, killing 26 people before turning the gun on himself.
Proctor told the station that resource officers are assigned to all the schools within the county and that the department planned to revisit school safety measures following the Newtown tragedy.
Johnson is charged with disorderly conduct, a misdemeanor. He is being held without bond in the county jail. It is unclear if Johnson has retained an attorney.