Chile has strict rules for wearing masks in all public places, and violations are punishable by penalties including fines and even imprisonment.
The president explained that he had been walking alone on the beach near his home in the chic Chilean resort of Cachagua when a woman recognized him and asked for a photo together.
The selfie shows the president and the woman standing very close to each other on a sunny day, without wearing masks.
The blunder-prone Pinera was previously photographed at a pizza party during the night-time inequality protests that broke out in Santiago last year. He was later seen posing for photos in the square that had been the focus of the demonstrations after the pandemic forced protesters to stay at home.
The virus peaked in May and June in Chile, during the winter in the Southern Hemisphere, and then disappeared through November. However, the number of cases is on the rise again, creating new restrictions and quarantines.