Suggesting to swap the keyboard (preferably for a PS/2 one). I'm testing a few 486 mobos right now (PVI-486SP3 rev. 1.2 & 1.8, BIOS v.0307 and GA-5486AL rev.2A I suppose)

- both have no problems with a native 5-DIN keyboard (Chicony).
- both have no problems with PS/2 to 5-DIN convertor (random brand).
- the GA-5486AL board displays the same behavior as yours using HP PS/2 keyboard with the 5-DIN convertor; the PVI-486SP3 does not.

I think (since your rig seems to be fairly ''new'' for serious retro) you're facing a compatibility issue as I was. FYI HP is the worst choice for old hardware to be used, meaning just the keyboard and mouse. HP's USB mice are not compatible with those green USB to PS/2 convertors for example.

But it might be a malfunctioning onboard connector you're using, I suggest to obtain a PCI usb card to verify whether a physical issue is present or a firmware issue of your accessories.

Have you ever seen a Keyboard error during the POST procedure of your rig?

Also check your memory timing settings and other BIOS features for possible inconvenient values. Do you have any other problems with this rig, like a BSODs or random hick-ups, just something that doesn't look OK?

yep, it's strange.. even if I do a clear cmos same thing happens. I also tried with a native PS/2 keyboard, and well, the bios doesnt say anything about not having a keyboard =(

Check the fuses on the board, on rare occasions they do fail and it is possible that the fault could be something else. This is why it is best to have extra boards on hand.