My mom is a U.S. Citizen I got my permanent resident card 5 years ago, about to be six years. Can I apply for citizenship?

You would be eligible to apply for naturalization of you are 18 years or older. You may already be a United States citizen depending upon how old you were when your mother naturalized. If you are already a citizen by operation of law, you would simply need to request a certificate of citizenship. You can read more about deriving citizenship from a parent and naturalization at http://myattorneyusa.com/citizenship-and-naturalization.