It only rotates when it is scanning.

Open the avastUI, Real-time Shields and check the File System Shield (FSS) view and it should show the files that are being scanned, that should give you an idea of why the FSS is scanning and why the icon is rotating.

If nothing on the FFS view, check the other shields to see which the activity is on.

Do you happen to be doing anything in the background, e.g. P2P download, collecting email, windows indexing service, etc. ?