My father passed away Jan2013. A company has issued a refund check to him. Am I able to cash this check or should I return it to the company?

Your father's estate can cash the check, through its legal representative (executor, administrator, etc.)  If you have not been appointed by a Court as the legal representative of your father's estate, you technically should not cash the check, especially if it is for a substantial amount and you are not your father's only heir.  If it is for a minimal amount, however, and you are either your father's sole heir or you share the proceeds with all other beneficiaries, then nobody will be hurt if you do cash it (assuming the bank lets you; if the bank is aware that your father has died, it will not let you cash the check), and you almost certainly won't get into any trouble.