Your supervisor might not be able to give you a lot of information, but s/he does owe you clearer direction. You can probably assume that a complaint has been officially filed against you with HR by or on behalf of the person you must stay away from. As a result, you are the target of an employee investigation.
Usually, allegations of discrimination, harassment, threats of workplace violence, and other intense and high stakes issues involve the requirement that the supervisor refrain from working with a specific subordinate until the matter is resolved. It’s normal for the Person Complained About (PCA) – that’s you – to be dislocated rather than force the complainant to switch shifts or otherwise modify their work.
You’re in limbo right now because you know very little. Tell your supervisor that you understand they can’t say anything but you are guessing a complaint has been filed against you by the employee you’re not allowed to work with. Don’t expect him or her to say yes or no, but tell them you need more direction from than “hang tight.” (In truth, your supervisor is likely getting their direction on this from HR and will need to go back to them on this. That's okay.)
Here are some things you may need to know: Are you supposed to report to work at all? If so, when, what job/shift/location, and for about how long? If not, will you be paid? Will you get an opportunity to understand at some point what the problem is and present your perspective?
You’re in an unenviable spot. If you happen to run into the complainant, try to respectfully avoid them or simply nod to acknowledge them and quickly go your separate ways. Don’t discuss the complainant at all with ANY of your coworkers or subordinates. And finally, when this is over, don’t retaliate. I know that is awkward to say, “Don’t treat them differently,” but try to figure out a way to make things right no matter who was in the wrong. Being a first-line supervisor is really difficult!