Susie Buffett, 66, sat next to someone for two hours, who had just returned from a trip to Spain, the newspaper said, adding that the individual developed mild symptoms and then tested positive for COVID-19. Buffett said she feels fine and is "not the least bit worried," the paper noted.
She also said she had not been around her billionaire investor father, Warren, since her potential exposure, according to the news outlet.
COVID-19 is caused by the new coronavirus that was first detected in China's Hubei province. It has affected at least 153,000 people around the world and killed more than 5,700 people, according to the latest data from the World Health Organization.
WHO has classified the outbreak as a global pandemic.
Last week, U.S. President Donald Trump declared a national emergency that is said to free up as much as $50 billion in financial resources to assist affected Americans. The number of cases in the U.S. is rising steadily; at least 3,774 people have been infected and close to 70 have died so far, according to data collected by Johns Hopkins University.
Countries in other parts of the world have also stepped up efforts to contain the pandemic, including total lockdowns in places like Italy.