There are two different types of medical assistant job certification. One is an RMA certificate and the other is a CMA certificate. These certificates are awarded by two different agencies, but have very similar programs.
To become certified in either of these programs it will be necessary to complete an accredited training program. This can be done at any accredited institution (both online and in person) that is convenient for you. Then you will have to complete a written exam put on by the certificate awarding agency.
While it is not required that you be certified to have a medical assistant job, many have found benefits in becoming certified. These potential benefits include finding employment as a medical assistant as well as performing more confidently as a medical assistant.