The second revision of Windows 95 supported USB - it may be that you have this version which would support keyboards and mice (but not much else) if you give it a PCI USB card. You'll need a card that's supported by Windows 95 too - no idea if that's a big ask or not.
Failing that, many older PS/2 mice supported the serial protocol with a simple adaptor, and PS/2 and AT keyboards are almost identical protocol-wise so you just need an adaptor to use that too...
Really though, I'm sure you could find a more up-to-date PC for about the same price as a USB card which would have USB already on it. Only 2 weeks ago I threw a Pentium 2-350 with Windows 98 into a recycling skip (along with a Commodore 486 by the way...), basically because it was worthless and there was no software on it that I couldn't run in DOSBox on my XP machine. But it had USB, CD-RW, 128MB and some other good stuff in it.
