It depends on where (in which state) your nonprofit is soliciting contributions, but for most nonprofits the answer will be yes, you need to register. All but 11 states require nonprofits to register with a designated state agency before the organization can solicit contributions from residents of the state. These registration rules are followed in every state except Delaware, Idaho, Indiana, Iowa, Montana, Nebraska, Nevada, South Dakota, Texas, Vermont, and Wyoming.
Solicitations can include any type of requests for donations by mail, phone, advertisement, email, or Internet, regardless of whether your nonprofit actually receives any donations. Learn more about nonprofit registration requirements -- and what your organization needs to do -- in Nolo's article Fundraising Registration -- Does Your Nonprofit Need to Register?