In a series of articles published in 1986 Derrida, and his colleagues studied two mean field treatments (the quenched and the annealed) for NKKauffman Networks. Their main results lead to a phase transition curve K c 2 p c (1 − p c ) = 1 (0 < p c < 1) for the critical average connectivity K c in terms of the bias p c of extracting a "1" for the output of the automata. Values of K bigger than K c correspond to the so-called chaotic phase; while K < K c , to an ordered phase. In [F. Zertuche, On the robustness of NKKauffman networks against changes in their connections and Boolean functions. J. Math. Phys. 50 (2009) 043513], a new classification for the Boolean functions, called Boolean irreducibility permitted the study of new phenomena of NK -Kauffman Networks. In the present work we study, once again the mean field treatment for NK -Kauffman Networks, correcting it for Boolean irreducibility. A shifted phase transition curve is found. In particular, for p c = 1/2 the predicted value K c = 2 by Derrida et al. changes to K c = 2.62140224613 . . . We support our results with numerical simulations.