I graduated from a U.S university one year ago. If one year after my graduation a person or a group of persons claim(s) to the university that I harassed them (verbally or physically), could this claim lead to the revoking of my degree?
Universities and colleges are governed by their own rules. I would be surprised if a degree revocation would be possible based on bad behavior alone, even if the bad behavior would be criminal. Bad behavior is usually sanctioned in other ways such as expulsion or suspension, or by going through the criminal or civil justice system. After graduation, the institution itself is usually not in a position to sanction the now ex-student in a meaningful way. They could kick the ex-student out of the alumni association and send a letter of reprimand, maybe. Redress for a victim would need to go through the criminal or civil court system.
Degree revocation usually needs to be based on some type of grievous academic misconduct, such as repeated cheating on examinations or serious plagiarism in a thesis.
However, without knowing your institution and the rules of that institution, nobody here can answer this question.
People can claim whatever they want, and a claim by itself should be no basis for disciplinary action. Now, if their claim is substantiated with evidence, the consequences will depend on the severity of your actions. "Verbal or physical harassment" (your words) covers a wide range of behavior, from saying something others don't like, to stalking (I don't really know what other behaviors could be incldued under "physical harassment": if you physically touched people, that'd be assault.) It is unlikely to result in the revocation of a degree at any university I know of. But there might still be consequences if the act was illegal, e.g. if you stalked, you might still get a restraining order issued against you, etc.