WASHINGTON — In rare public remarks, Justice Clarence Thomas on Monday dismissed what he called “this rumor that I was retiring.”

“I have no idea where this stuff comes from,” he said.

Justice Thomas, in a relaxed and reflective mood, was interviewed by David Rubenstein, a financier and philanthropist, in the Supreme Court’s courtroom as part of a series of lectures sponsored by the Supreme Court Historical Society.

“I really don’t have a lot of stress,” Justice Thomas said cheerfully. “I cause stress.”

Justice Thomas, 70, joined the court in 1991 and is now its longest-serving current member. Political scientists say he is the most conservative justice in the Supreme Court’s modern history.

He often writes concurring and dissenting opinions that are joined by no other justice. So far this term, he has called for the court to reconsider New York Times v. Sullivan, the landmark libel ruling, and argued that the fight for abortion rights shares roots with the eugenics movement.