Alexander Mercurio, an 18-year-old from Idaho, was arrested for allegedly planning attacks on local churches in support of the Islamic State (IS) group.
He intended to carry out the attacks with guns, explosives, knives, and a pipe, with a plan to move from church to church until being killed.
Mercurio faces up to 20 years in prison for attempting to support a foreign terrorist organization.
The FBI became aware of his intentions through messages he sent, expressing loyalty to IS and outlining his violent plans.
Law enforcement seized weapons and other items from his family home during a search.
The arrest follows a warning from authorities about potential threats to public gatherings in the US, prompted by recent attacks claimed by IS.
