A previous suspect in the case suggested James Everett Dutsche was trying to frame him, CNN reported.
Tupelo Police Chief Tony Carleton said the arrest was carried out by the FBI, WTVA-TV in Tupelo reported. Carleton would not say what the specific charges are.
Letters containing ricin sent to Obama, U.S. Sen. Roger Wicker, R-Miss., and a judge in Mississippi were intercepted before they reached their targets. Ricin, a deadly poison, can be extracted from castor beans, although manufacturing the purest form is difficult.
Sources told WTVA Dutsche will be held in the Lafayette County Jail pending a court hearing Monday.
Paul Kevin Curtis of Corinth, Miss., was arrested last week. He was released Tuesday after the charges were dropped.
Investigators searched Dutsche's Tupelo home Tuesday and his martial arts studio, The (Jackson, Miss.) Clarion-Ledger reported. At the time, Dutsche denied sending the ricin letters or trying to frame Curtis.
"I guess Kevin got desperate," he said. "I feel like he's getting away with the perfect crime."