"It's very clear they are preparing for an announcement," the New Hampshire Republican, speaking on the condition he not be named, said Thursday. "They are looking for talent."
The Associated Press first reported on Thursday that Brown has been reaching out to potential staffers.
Brown will speak Friday at the Northeast Republican Leadership Conference in Nashua, amid a roster of potential presidential candidates like Louisiana Gov. Bobby Jindal and former Sen. Rick Santorum. The Washington Republican said Brown will announce his exploratory committee there.
Brown will begin the race as an underdog. A recent Suffolk University survey conducted for the Boston Herald showed Shaheen leading Brown by a 52 percent to 39 percent margin.
But if Brown enters the race, it will represent another last-minute success for national Republicans hoping to put Senate seats in play. Last month, Republicans persuaded Rep. Cory Gardner (R) to mount a bid against Colorado Sen. Mark Udall (D). Counting Massachusetts, Republicans are mounting serious challenges to Democratic incumbents in nine states. Polls show Republican candidates leading in three additional states where Democratic incumbents are retiring.