It should work fine. I've used one of those keyboards with a 2009 Mini in the past, but not with El Capitan.Will the original Apple Wireless Keyboard (the one with white plastic keys in a clear plastic shell - A1016) work with a Late 2009 Mac mini on El Capitan?
Thanks!
If you already have the keyboard, try it.
If you DON'T have the keyboard (haven't bought it yet), I suggest you try a WIRED keyboard instead.
It should work fine. I've used one of those keyboards with a 2009 Mini in the past, but not with El Capitan.