The 71-year-old Oscar-winner performed around 10 tracks, including 'Memory', 'You Don't Bring Me Flowers' and 'People', before being whisked off stage just as stealthily as she arrived, reported Contactmusic.
Around 4,000 Baron shareholders enjoyed the hour-long afternoon concert.
Recently the 'Funny Girl' star said she never followed her family advice and always wanted to become an actress.
"My mother told me I should be a secretary, but I wanted to be an actress from when I was very young. Looking back I think it was maybe an escape," she had said.