That code is for problems relating to the O2 sensor that is in back of the catalytic converter, but the sensor may not actually be the source of the problem. Before you go to the trouble of replacing the sensor, check for an exhaust leak, as that can also trigger that code. Many chain muffler shops will check your exhaust system without charge.
A disconnected wire running to the sensor can also be the reason for that code.
After 11 years, it is certainly likely that the sensor is bad, but by checking the things that I listed, you may resolve the problem. If you do replace the sensor, I suggest that you avoid the “universal” ones, and instead buy a Denso-brand O2 sensor specifically made for an '03 Accord. A good auto parts store, like Napa, should have this for less cost than what a dealership would charge.