The effect of a strong electric field on the dielectric properties of nominally pure LiNbO3 crystals of congruent composition in the low-frequency region is experimentally investigated. It is shown that an external static electric field, directed along or antiparallel to the polar axis of the crystal, as well as a field of pyroelectric nature at a field strength of up to 14 kV / cm within the error does not affect the dielectric properties of the crystal in the low frequency range.