  We present a minimal inverse seesaw mechanism by resorting to a $U(1)_{B-L}$
gauge symmetry. In order to cancel the gauge anomalies, we introduce seven
neutral fermions among which four participate in the inverse seesaw to induce
two nonzero neutrino mass eigenvalues, two forms a stable Dirac fermion to
become a dark matter, while the last one keeps massless but decouples early. In
this inverse seesaw, two neutral fermions are the usual right-handed neutrinos
while the other two have a small Majorana mass term. An additional seesaw
mechanism for generating these small Majorana masses also explains the cosmic
baryon asymmetry in association with the sphaleron processes.
