  We study the Moyal commutators and their expectation values between vacuum
states and non-vacuum states for free scalar field on noncommutative spacetime.
Then from the Moyal commutators, we find that the microcausality is satisfied
for the linear operators of the free scalar field on noncommutative spacetime.
We construct the Feynman propagator of Moyal star-product for noncommutative
scalar field theory.
