If you're looking for just a Digital to Analog converter box for converting the free Over-The-Air digital broadcasts to an analog signal that your older TVs can accept, then no. You do not require an account with Comcast.
If you are currently receiving Comcast channels over your cable line and you do not currently have a subscription to Comcast (Comcast either didn't or couldn't disable the signal to your residence) and you do not care for any other channels, then no. You do not require an account from Comcast (though since you would be receiving their signal, you should have an account).
If you are currently receiving Comcast channels over your cable line and you do want to receive those channels that Comcast has started encrypting, then yes, you will require an account with Comcast and lease one of their set top boxes.
-Wolf sends