The regularities of the existence of the different electret state (ES) types in PbMg1/3Nb2/33/O3 (PMN) single crystals are investigated. The effects of inducing birefringence and piezoelectric activity by the electret charge field in a macroscopically non-polar PMN State are found. A model satisfactorily describing the ES relaxation in PMN is developed, The Poole-Frenkel effect arising in the high internal fields of electret charges contributes greatly to the ES relaxation.