Private equity firms Blackstone Group LP (BX.N), TPG Capital [TPG.UL] and Advent International are interested, the sources said.
Some potential suitors, such as Bain Capital, had been interested earlier but are no longer in the auction, they said.
RadioShack has been exploring strategic options and hired Goldman Sachs (GS.N) earlier this year to advise it, sources said.
A sale process for the firm has been moving slowly, some sources said. It remains unclear if a deal will eventually be done.
RadioShack, which has a market value of about $2.7 billion, has been focusing on its wireless business to offset weak sales of products like TV converter boxes, video game systems and batteries.
The sources declined to be identified because the process has not been made public.
Goldman Sachs was not immediately available for comment. Advent said it “does not comment on market rumors or speculation.” The other private equity companies declined comment.
RadioShack, which is trying to rebrand itself as “The Shack,” declined to comment.
Shares of RadioShack hit a high on Friday of $21.80 before falling to $20.93 in midday trading. The stock traded at $21.49, down 12 cents, or 0.56 percent, on the New York Stock Exchange in early afternoon. (Reporting by Megan Davies in New York and Jessica Hall in Philadelphia; Editing by John Wallace, Phil Berlowitz)