Is this normal 737 AT behavior ?

I've setup my Active Sky with DWC and I'm noticing a lot of AT movement on cruise ... it rapidly switch from 78% NG to 80% to maintain FMS speed but it's very annonying and unnecessary because I simply cut off AT and maintain 80.5% and just live with the airspeed juggling +/- 2-3 kts, or am I dead wrong and in real life the autothrottle is always moving and trying to maintain +/- 1kts. Eric Blais