Honda Accord 2000

The check engine light came on last August. When we tested it, it said the catalytic converter was not working as well as it should. This surprised me because it’s a low mileage car (under 164,000 at this time) that doesn’t burn much oil. We’ve already tried resetting the check engine light to see if it was a fluke, but the light keeps coming back on with the same message.
What should I do? Does the catalytic converter really need to be replaced? or is it just a faulty sensor?