Can't say for sure without being able to examine the message, but chances are about 99 out of 100 that it's a phishing email, a scammer attempt to steal login and account information. If you check your email with Comcast's Xfinity Connect webmail, look for the XFINITY Verified Email logo next to any message that claims to be from Comcast/Xfinity (see https://www.xfinity.com/support/articles/comcast-verified-email).
Please see Comcast Email Phish or Legit? How to Tell (and rules for posting) for more information about identifying, reporting, and posting phishing emails. The article is somewhat out of date, but still useful.
Samples of recent phishing messages can be found at https://internetsecurity.xfinity.com/help/alerts/ under "Top Phishing Scams".