95 Legacy Wagon Trouble code

I just scanned for a trouble code and it comes back P0420, Catlyst System Efficiency Below Threshold (Bank 1). Is this a clogged Catly. Converter? The 95 Wagon has 200,000 miles on it now. This engine light has been going in and out for over 2 months now. I have also noticed a drop in MPG's. Besides this the car runs great, no other problems. Thanks for any input.