It can be awkward to brag about yourself, so while this question may seem weird, it's really the HR professional's tactic for hearing how your current boss views you in a work environment. To feel less uncomfortable answering this question, thoughtfully consider your last performance review, and use direct quotes from your boss in your answer.
For instance, you might say, "Well, during my last performance review, my current manager told me she appreciates how quickly I take constructive feedback and use it to improve in my role. She's grateful that she never needs to repeat areas of improvement to me -- once she gives me feedback, I take it seriously and make sure she never needs to bring it up again. She has also described me as diligent and trustworthy, two aspects I believe are critical for excelling in any role."