PS/2 keyboard does not take much (any?) power over the PS2 connector. It should have no lights, etc. So how do you know it is in powered state?
Besides, the keyboard is a device that should wake your PC out of sleep mode, so for that it will remain in a low-power sleep state.
Since you didn't even bother to mention the make or model of the keyboard, the computer or the motherboard, how do you expect advice on what can be done from the BIOS?