The three stores are at 10861 Weyburn Ave. in Westwood; 4120 E. 4th St. in Ontario; and 2857 Park Ave. in Tustin.
Eight of the 50 stores had already been tapped for closure. Of the 42 locations announced Saturday, Best Buy said most would be shut by May 12; three additional locations will close by late summer.
"This was not an easy decision to make," the company said in a statement. "We chose these stores carefully, and are working to ensure the impact to our employees will be as minimal as possible, while serving all customers in a convenient and satisfying way."
The company, which earlier this week announced that chief executive Brian Dunn was stepping down, said it was working to help employees find other positions at Best Buy.
Best Buy, which has been hurt as more consumers go online to purchase electronics, said the store closures were intended to decrease overall retail square footage and increase points of presence "for increased flexibility." It said it was focused on remodeling some locations and building out its Best Buy Mobile small-format stores throughout the U.S.