The problem of active shielding of some domain from the effect of the field generated in another domain is considered. The active shielding is realized via the implementation of additional sources in such a way that the total contribution of all sources leads to the desirable effect. Mathematically the problem is reduced to seeking the source terms satisfying some a priori described requirements and belongs to the class of inverse source problems. From the application standpoint, this problem can be closely related to the active shielding of noise and active vibration control. In contrast to many other approaches, it does not require either the knowledge of Green's function or any information on source distribution and surrounding medium. It is also important that along with undesirable field to be shielded a desirable filed is accepted in the analysis. The solution of the problem requires only the knowledge of the total field at the perimeter of the shielded domain. The active shielding sources are obtained for the nonlinear statement of the problem. It is represented in the form of a simple layer. To take into account the diffraction effects of the secondary (additional) sources, some boundary value problem is to be solved. It is formulated via the difference potential method. For this purpose, the method is generalized to nonlinear formulations and the theory of distributions.