  We explore the features of the $U_A(1)$ and chiral symmetry breaking of the
Nambu--Jona-Lasinio model without the Kobayashi-Maskawa-'t Hooft determinant
term in the presence of a parallel electromagnetic field. We show that the
electromagnetic chiral anomaly can induce both finite neutral pion condensate
and isospin-singlet pseudo-scalar $\eta$ condensate and thus modifies the
chiral symmetry breaking pattern. In order to characterize the strength of the
$U_A(1)$ symmetry breaking, we evaluate the susceptibility associated with the
$U_A(1)$ charge. The result shows that the susceptibility contributed from the
chiral anomaly is consistent with the behavior of the corresponding $\eta$
condensate. The spectra of the mesonic excitations are also studied.
