Obama, unaware of being caught over an open mic, was chatting with UN Special Rapporteur Maina Kiai during an event at United Nations headquarters in New York.
"I hope you quit smoking," Obama said as the two men greeted each other.
Kiai admitted to the president that he hadn't given up smoking altogether, to which Obama answered that "I haven't had a cigarette in probably six years."
"That's because I'm scared of my wife," the president confided during an exchange that was aired on CNN.
Obama acknowledged in recent years that he was struggling to stop smoking, while the first lady, a promoter and champion of healthy living, was one of the people who most insisted on it.
Obama was still a smoker when he had his first medical checkup as president in February 2010.
However, months after being elected president, he admitted that he still smoked from time to time. It wasn't until 2011 that doctors confirmed that Obama was leading a smoke-free life.