Video report by ITV News Scotland Correspondent Peter Smith
Ms Sturgeon apologised for the breach and told MSP's: "I want to be clear today that regardless of the circumstances I was in the wrong, there are no excuses.
"These rules do apply to me just as they do everyone else, and the rules really matter"
"I am kicking myself very hard, possibly harder than my worst critic ever could."
A photograph published in the Scottish Sun showed the First Minister chatting to three women in a bar while standing at a distance but without wearing a mask.
Under Scottish Government coronavirus rules, customers in hospitality venues must wear a face covering except when seated and must wear one when moving around.
Ms Sturgeon was attending a funeral wake for a Scottish Government civil servant.
She concluded her statement to MSPs, as always, with a reminder of the Scottish Government’s FACTS guidance on coronavirus.
“With an enormous dose of humility, let me remind you and most importantly myself, of FACTS,” she said.
“Use Face coverings, Avoid crowded places, Clean your hands and surfaces regularly, keep Two metres distance from other households and Self-isolate and get tested if you have symptoms.”
The Scottish Sun reported that she was at the Stable Bar and Restaurant after attending a funeral at the nearby Mortonhall Crematorium.Under coronavirus regulations introduced on September 14 in Scotland, face coverings for customers and staff are mandatory when entering, exiting and moving around hospitality venues.
The rules state: “There is an exemption for when customers are seated for the service of food and drink and for back of house roles such as kitchen staff or staff who are behind protective screens separating them from customers.”
Those who breach the face covering rules can face a £60 fine.
Scotland’s Justice Secretary Humza Yousaf tweeted: “FM has approached pandemic by being upfront from v beginning.
“She has apologised for accidental lapse (which I suspect most of us have had one over last 9 months).
“I’ve known her for 15yrs & she is her harshest critic. I am sure most ppl will understand, accept apology & move on.”