Based on MHD concepts, we explain and prove that a self-confined plasma ball imbeded in a constant pressure p0 can be in equilibrium as well as stable states. Besides, it is found that the equilibrium states can not be force-free configurations. The conclusion that the average pressure inside the plasmaball is less than p0 is drawn from the calculation. Furthermore, we point out that the condition for the stability against local perturbations is satisfied, even magnetic shear is weaker in the plasmaball, which implies that the self-confined plasma ball can be expected to have some favourable MHD stability characteristics.