We show that a standard model gauge singlet fermion field, with mass of
order keV or larger, and involved in the inverse seesaw mechanism of light
neutrino mass generation, can be a good warm dark matter candidate. Our
warm dark matter candidate can also be produced non-thermally, directly
from the decay of the moduli field during reheating. In this case, the
right amount of relic abundance of our dark matter candidate is obtained,
while the reheating temperature is high enough as to be consistent with
Big Bang nuceosynthesis.