  A relativistic complex scalar boson field at finite temperature $T$ is
examined below its critical Bose-Einstein condensation temperature. It is shown
that at the same $T$ the state with antibosons has higher entropy, lower
Helmholtz free energy and higher pressure than the state without antibosons,
but the same Gibbs free energy as it should. This implies that the
configuration without antibosons is metastable. Results are generalized for
arbitrary $d$ spatial dimensions.
