If you're not doing much of anything else, Android System or OS will often be the highest on the battery use list, because the system still has to run. And if you're not doing anything else, then it makes sense for the system to use up the most battery in proportion to everything else.
The important question here is if your battery is draining unusually fast. Charge up to 100%, then let it drain to 20-30% with normal usage, without charging in between. Then show us:
1. The main Settings>Battery screen.
2. The fullscreen battery graph screen (which shows Awake time and Cell Signal Strength).
3. The Screen category (to see total Screen On time).
4. The Cell Standby category, if present (to see Time Without Signal).