Having an active nursing assistant certification in Ohio makes you eligible to ask for certification by reciprocity in Arkansas. First contact the Arkansas Office of Long Term Care at (501) 682-1807 to request the nurse aide reciprocity forms. The Arkansas LTC Office will contact you and let you know if you need to sit for the CNA certification exam or if challenging the exam is not necessary.
As far as I know only candidates with an inactive certification are required to take and pass the certification exam. The application to challenge the Arkansas nursing assistant exam can be found here. Send this application only if you are required to do it after you have been approved for reciprocity.