The bottom line is that you will always be learning as an entrepreneur. As a scientist and engineer, I have done startups for 20 years. For the first 10 years (and 2 startups) I had no formal business training, then I decided to go back to get my MBA in Entrepreneurship. I chose this route to get a firmer foundation on the business side as my formal education (BS Chemical Engineering, PhD Biomedical Engineering) provided very little background in business-related activities. Going this route has helped me converse in both highly technical vernacular and business-focused discussions. I work with medtech and biotech startups, so such capability is crucial.

Aside from the formal education, going back to school for business training can also provide you with other benefits such as broadening your network, access to discounts (as a student), ability to pursue many business plan competitions to jumpstart your company, and low-cost or free advice from your school and it's connections regarding everything from legal issues to business formation (depending on the school). However, you may not need such support depending on the type of business you plan to launch.

Going back to school takes commitment of both time and money which you will be taking away from launching your new venture. It's not necessary for you to go back to school, but, depending on your career goals, your learning preference (formal, hands-on, etc.), and your business concept, it could be beneficial.

As others have mentioned, you may only need to attend some local business networking meetings and take some classes through your local Small Business Administration office.

Best of luck!