No. Not all employers require certification however it is preferred. In addition, according to the American Academy of Professional Coders (AAPC), certified coders and billers earn 17% more than non-credentialed coders. There are many types of certifications a medical coder and biller can obtain.
If you are unsure if you want to become certified in medical coding, look at the job openings in your area and with the companies you plan to apply with to see what they require. If they require or prefer certification, then it is probably a good idea to go ahead and get certified.