USB has power even with PC is off

I have a very strange problem, at least I think its a problem. I was about to go on my computer because I had to transfter something from my flash drive onto it. I plug my flash drive into the USB port and am about to push the power button on the PC to turn it on when I notice that the LED on the flash drive is lit up. As far as I know the USB ports shouldn't be getting any voltage unless the PC is turned on. Any ideas?

For those who want to know, this is a home built PC and its the first time i've noticed this happening.

 

that's normal most new pc keep power to the usb ports when power'd down there should be a switch on the psu to cut the power if it really bugs you

 

oh ok, thanks. it doesn't bother me, it just got me worried because i've never heard of that before, but since its normal then i guess i have nothing to worry about, thanks again