Cerberus specialises in distressed companies and is understood to have asked to look at BlackBerry's accounts in order to gather the information needed to make an offer.
The firm, whose interest was first reported by the Wall Street Journal, declined to comment.
BlackBerry publicly put itself up for sale this summer after a failed turnaround bid by chief executive Thorsten Heins, but has so far attracted only one bidder.
A preliminary agreement to sell the company for $4.7bn (£2.8bn) to former board member Prem Watsa was signed last week. Watsa's investment fund Fairfax Financial has until 4 November to raise required capital.
BlackBerry's shares traded up on news of interest from Cerberus, rising around 1% to nearly $8, but their value is still well below the $9 a share being offered by Fairfax.
A spokesman for the company said: "We do not intend to disclose further developments with respect to the process until we approve a specific transaction or otherwise conclude the review of strategic alternatives".
Heins launched a new generation of BlackBerry phones in January, but the innovation left consumers cold. While many BlackBerry loyalists still prefer its physical keyboard to touch screen machines, developers have not embraced the new BB10 devices, meaning many popular games, social and media sapplications are not available on the phones.
In 2011, BlackBerry still accounted for 14% of all smartphone sales worldwide, but according to industry analyst IDC its share had fallen to 3% by the second quarter of this year.
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image: © Sophie Schieli