Using a method of free energy minimization，the spin wave of ferromagnetic （FM）/antiferromagnetic （AFM） bilayers was investigated，in which the net magnetization of AFM layer has been considered. In this model，the thin FM layer is taken to be a single crystal with cubic and uniaxial magnetocrystalline anisotropies，but AFM layer has only single uniaxial magnetocrystalline anisotropy and its thickness is finite. Numerical calculation shows that there are two modes of spin waves：namely the acoustic mode and the optical mode. Moreover, only when there is net magnetization of AFM layer can the optical mode be observed. There are two branches of FMR curves，i.e. the branches of weak and strong external field，which are distinguished by the critical field，while the critical field depends on the exchange bias field，the magnetization and thickness of AFM layer. The effect of the exchange bias field on the optical mode is more obvious than that on the acoustic mode，while the effects groduced by net magnetization and thickness of AFM layer cant be distinguished. However，when the net magnetization of AFM layer is neglected，only an acoustic mode is observed.