Prosecutors said he planned to use the bomb to kill himself and draw attention to a political system called sortition, in which public officials are chosen randomly rather than elected.

It was not immediately clear whether Rosenfeld had an attorney. A message left with the federal public defender's office in White Plains, which often represents newly arrested criminal defendants, wasn't immediately returned.

The FBI raided Rosenfeld's home Tuesday and found a functional bomb in his basement that consisted of black powder inside a plywood box, according to a criminal complaint.

Agents also found empty canisters of black powder often used in firearms and artillery, the complaint said.

The FBI said in court filings that Rosenfeld, after being pulled over on Tuesday, confessed to ordering large quantities of black powder over the internet and having the substance delivered to "a location in New Jersey."

Rosenfeld took the black powder to New York, constructed smaller explosive devices and conducted test detonations, according to the criminal complaint.

William Sweeney Jr., the assistant director of the FBI's New York field office, said in a statement that Rosenfeld intended to "detonate a large explosive to kill himself and draw attention to his radical beliefs."

"Had he been successful, Rosenfeld's alleged plot could have claimed the lives of innocent bystanders and caused untold destruction," Sweeney said in the statement. "Fortunately, his plans were thwarted by the quick action of a concerned citizen and the diligent work of a host of our law enforcement partners and the FBI's Joint Terrorism Task Force."

Rosenfeld had an initial court appearance before a magistrate at a federal courthouse in White Plains on Wednesday afternoon.