According to the New Hampshire Union Leader, Bass is exploring a bid.
"But I'm not ruling out the possibility of running for the Senate. I'm thinking about it, but I haven't made up my mind," he said, adding that he's speaking with advisers and supporters about running.
Bass lost his seat to Rep. Ann McLane Kuster (D) last cycle by 5 points, a race that would've likely been closer had a libertarian candidate not split the GOP vote.
He was initially believed to have ruled out a bid, but following state Senate Majority Leader Jeb Bradley's decision not to run, Bass reconsidered his initial decision.
The Union-Leader is also reporting that former state Sen. Jim Rubens is expected to announce his plans to run for the GOP Senate nomination on Sept. 18.
If both Rubens and Bass jump in, Granite State Republicans could see a three-way primary, with conservative Karen Testerman also expected to enter the race.
While Republicans believe Shaheen to be vulnerable, citing ObamaCare's unpopularity in the state, she's boasted a strong approval rating in every poll this year and has already raised more than $3.5 million for her reelection bid.