  CP violation from physics beyond the Standard Model is investigated in
$B_{l4}$ decays: $B\to D\pi l\bar{\nu}_l$. In the decay process, we include
various excited states as intermediate states decaying to the final hadrons,
$D+\pi$. We consider the semileptonic decay to a tau lepton family as well. The
CP violation is implemented through complex scalar--fermion couplings in the
multi-Higgs doublet model and scalar-leptoquark models beyond the Standard
Model. With these complex couplings, we calculate the CP-odd rate asymmetry and
the optimal asymmetry. We find that for $B_{\tau 4}$ decays the optimal
asymmetry is sizable and can be detected at $1\sigma$ level with about
$10^6$-$10^7$ $B$-meson pairs, for maximally-allowed values of CP-odd
parameters in those extended models.
