Honda motor: Need help, B16a RPMs are randomly decreasing/stuttering?

[Melanie]

Ok, so basically I was driving to my buddys place on the highway, going a steady 110km/hour. I had been driving like this for about an hour straight, when all of a sudden I noticed my motor nudging a bit. At first I thought they were just bumps in the road, but the suspension was not reacting to any bumps. These nudges didnt occur very often, so it was hard for me to tell if it was the motor or bumps, but eventually i caught a glimpse of my RPMs nudging (I was at 4000RPMs and it dropped to 3000RPMs, then rapidly go back to normal) They felt almost like a stutters, but the motor continued normally. They didnt occur very often, but I know this is not normal. By the way - I just recently got an oil change, if that matters. Anyways any help would be great, thanks.