All depends on what level of Comcast service you are paying for and/or how you might define "good".
If you are paying for 6 Mbps service, then, yes they are good.
FWIW, you might also want to try another server location for the Speedtest.net test. Try the Comcast Chicago server.
Note: that Speedtest.net result can vary depending on the server that you use. In theory, picking the Comcast server in Chicago will keep all your traffic on the Comcast network and give you the best test of what COMCAST is supplying you (their "stated" speeds are only really meant to be while you are on their network...one you hit the wide open Internet, then all bets are off).