The Maloof family is close to agreeing to sell the Kings to the Ballmer group, which hopes to move the franchise to Seattle in time for the 2013-14 season, Yahoo Sports cited league sources as saying. Reuters could not immediately confirm the accuracy of the report.
As part of the proposed deal, the Kings would play for two seasons in KeyArena - the former stomping grounds of the Seattle Supersonics - before moving into a new facility built with the help of a public financing deal already in place, Yahoo reported.
Ballmer, the NBA and representatives for Hansen all declined to comment.
The Sacramento Kings did not immediately respond to phone calls or emails seeking comment. Seattle city officials told Reuters they were aware of the rumors, but were not in a position to comment.
Seattle lost the SuperSonics franchise in 2008 when it moved to Oklahoma City and was renamed the Thunder. At the time, its owner faulted Seattle officials for not coming up with a plan to build a new arena.
Then last October, officials from Seattle - a stone's throw from Microsoft's corporate base in Redmond - signed off on a pact to bankroll a new NBA arena. That was built on an earlier agreement struck between would-be franchise owner Hansen, Seattle Mayor Mike McGinn and King County Executive Dow Constantine.
But McGinn was coy when asked about the report on Wednesday.
"I know as much as you do about the Sonics," McGinn told reporters at a re-election news conference on Wednesday. "But if it's true, ain't it cool?"
Industry observers said there remained a welter of factors that could undermine any potential agreement.
Hansen has spent millions of dollars on land south of downtown Seattle to house a new arena, though locating it there is contingent upon the outcome of an environmental assessment and a review of other potential sites.
"It's not a done deal. There are discussions, I'm told," said Marc Ganis, president of consultancy SportsCorp Ltd in Chicago, who is not involved in the deal. "There are lots of unknowns. I think $500 million sounds like the right range."
Sacramento Mayor Kevin Johnson, himself a former NBA star, also weighed in on the widespread reports on Wednesday.
"Bottom line Sacramento: it's not over," he tweeted. (Reporting by Jonathan Kaminsky and Sue Zeidler in Los Angeles; editing by G Crosse)