It could be. It's not unusual for Open Access journals to request a payment from authors; these are referred to as "article processing charges," and are a part OA.
However, if you have concerns about the legitimacy of a journal or publisher, try checking it out on the Scholarly Open Access website (http://scholarlyoa.com/). This site is maintained by a librarian, and keeps a running list of potential, possible, or probable predatory scholarly open-access journals.