Look inside "About this Mac" and then inside the USB section. You will find that there is a USB hub built into the keyboard. So yes you can plug stuff into it but notice the "max speed". That hub is only a USB version 1 hub, it is not the faster and more modern USB version 2 hub that is on the back of the computer. The keyboard is OK for things like mice and graphic tablets but not for a disk drive or scanner. Well it would work but it's slow.
But the exact details depend on the model of Mac you have. That is why there is the "About this Mac" feature.