SOLVED Had to update firmware http://www.coolermaster.com/peripheral/keyboards/masterset-ms120/ Go to Download sub-nav..I downloaded the 104key file. Plugged keyboard into Win10 machine, ran the .exe and it updated firmware. Keyboard now works on OS X 10.13.6 High Sierra.
I have the same issue with my masterset ms120 keyboard+mouse combo..the mouse works on my 2016 macbook pro (10.13.6 high sierra). The keyboard is not detected on my OS X but it works on my windows 10 PC. I am thinking a firmware update is necessary...created a support ticket with Cooler Master. Waiting to hear back from them. The firmware I found on their website doesn't seem to do anything..