School officials learned of the allegations on Tuesday and launched an internal investigation, according to a statement from Superintendent Eric Witherspoon to parents and the school community.
The school "took appropriate measures to inform the Evanston Police Department," the statement said.
It is now a police matter, according to the statement.
Authorities have not disclosed what the alleged inappropriate contact may involve.
Witherspoon said high school officials are cooperating with police during their investigation and will determine what further action is necessary according to district policy. He asked anyone with information about allegations against its staff to contact police at (847) 866-5000.