The suspect, a convicted felon, was indicted last month on weapons and counterfeiting charges, The Detroit News reported Friday.
The Rev. Wendell Anthony, president of the Detroit branch of the NAACP, and Scott Kaufman, chief executive officer of the Jewish Federation of Metropolitan Detroit, said FBI agents from Ohio told them their names were on a "hit list.
Agents said the list was found during December searches of the Toledo home and Bowling Green store of Richard Schmidt, 47, who served time in prison after being convicted in 1990 of manslaughter.
About 18 firearms, body armor and more than 40,000 rounds of ammunition were discovered during the searches, the FBI and U.S. Attorney's Office for the Northern District of Ohio said.
Anthony said his group had received threats in the past and did not plan any extensive changes in security, but "we are very conscious now about our surroundings."
Kaufman expressed similar sentiments.
"We need to be smart, but we can't dramatically alter the way we operate because of people who hate us," he said.
Federal counter-terrorism agents were reported to have found evidence during the searches that indicated Schmidt might have had ties to white supremacist and neo-Nazi groups.