Yes it could be a bad hub assembly. BUT the common problem is that rust forms under the sensors. This causes the sensor to move away from the toothed wheel inside the hub, which causes the signal to fluctuate.
The easy solution can be DIY IF you have the tools. Pull the wheel/tire off. Then use a brush to clean all the dirt/crud from around the sensor. Get it as clean as you can. Now remove the bolt that holds the sensor in. Then GENTLY pull the sensor STRAIGHT OUT. if you try to pry it off center you will probably break it.
Once you have the sensor out use a rag or wood dowel to plug the hole in the hub. Now clean the rust and dirt from around the hole. Clean the tab and sensor very well also.
Now remove the plug from the hole and reinstall the sensor. Once you have the sensor in I like to use a brush and coat the sensor tab and around it with some non hardening sealer. This keeps the water/air out and slows the rusting.
Get the code cleared and then see what it does. I recommend cleaning BOTH sides so that they send the same signal levels.
Could be, but not as likely as either a dirty sensor face, or a misadjusted sensor. Remove, clean, and reinstall (to the correct clearance with the tone ring) and see if the problem goes away.
I do take it you don't have any other symptoms that would indicate a bad wheel bearing, right?
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