It doesn't necessarily mean that you have a virus, but that the email is considered to be spam.
You don't say what avast version you are using ?
Nor do you say what email client you are using ?
Presumably this is only on received emails, are they from the same source ?
This really should be in the
Avast Free/Pro/IS/Premier forum (or possibly the viruses & worms sub-forum if it is virus related) as this sub-forum relates to problem with the my.avast.com website.