ok, so do you have a rear O2 sensor in place? Lots of people don't have on, or have parts in place to fool the ECU, and sometimes they don't work perfectly.
if you have a fully working one in there maybe there is a problem.
if its a heater code, you need a new rear O2 sensor.
Now the only reason for a rear O2 is to monitor your catalyst, so if you have no cat, you don't need the rear O2, but you will have to disable the code in your software or always have a CEL on.
Personally I would run a good cat and run the sensor. At least on a real street car. Less headaches, no problems with aircare etc.
For a weekend warrior street car, maybe remove the rear sensor, the cat and disable the cel for that code, but make it so it can easily be put back it for aircare.