In this work, the authors study the nature of phase transition in a face centered cubic (FCC) antiferromagnet with Ising spins. The spin-glass character depends on the concentration p of ferromagnetic bonds randomly generated into the system. the authors introduce a new quantity MQ combined by the Edwards-Anderson order parameter Q and the standard magnetization M. Note that, it is impossible to obtain the susceptibility defined by the variance of Q or M, but the authors can do that for MQ. Using the standard Monte-Carlo and powerful Wang-Landau fiat-histogram methods, the authors carry out in this work intensive simulations with many value of p. The authors show that the first-order transition has been destroyed with a tiny amount of ferromagnetic bond p ~ 0.01. With increasing p, the antiferromagnetic phase changes into a spin glass, and then to ferromagnetic phase.