The evolution of neoclassical tearing modes (NTMs) is usually described by the generalized Rutherford equation allowing the mode growth from a finite level, which is referred to as a seed island. It is generally accepted that the seed island is induced by some MHD event, but sometimes the NTMs start without visible triggers. Here we discuss a possible role of the error fields in producing the seeds. The analysis is based on the Maxwell equations and Ohm's law for magnetic perturbations outside the plasma, which are considered in a cylindrical approximation. The plasma enters the problem via boundary conditions. In the model, its contribution is described by the decay/growth rate and the toroidal rotation frequency of the perturbation. The model also assumes a resonant harmonic in the spectrum of the error field. It is shown that the resonant field amplification near the stability boundary of the mode may be a mechanism resulting in the 'spontaneous' formation of the seed island. This applies to modes non-rotating or slowly rotating at the onset. In contrast to NTM seeding due to sawteeth, fishbones or edge localized modes, the considered mechanism needs a longer time. However, all the estimates give realistic values consistent with typical experimental conditions.