Yes, on is a Scrabble word!
...and is worth 2 points in Scrabble, and 3 points in Words with Friends
on
Adverb
1. With a forward motion
2. Indicates continuity or persistence or concentration
3. In a state required for something to function or be effective
Adjective
1. In operation or operational
2. (of events) planned or scheduled
What Scrabble words can I make with the letters in on?
2 Letter Words