If your car is has a manual transmisiton and it seems to be reving too hard this is because you need to select a higher gear or you already have top gear and you have a slipping clutch or massive...
It's not warmed up yet.
Broken/disconnected throttle cable
Your power brake booster is shot.
The vehicle speed sensor is a common failiure of this symptom. It is located on the gear box, often just un-plugging it will cure the problem