  This paper addresses the question of observability of neutral Higgs bosons
through the leptonic decay in a two Higgs doublet model (2HDM). Both scalar and
pseudoscalar Higgs bosons ($H,~A$) are considered. The model is set to type IV
to enhance the leptonic decay. In such a scenario, a signal production process
like $e^+e^- \to A^0H^0 \to \tau\tau \mu\mu$ or $\mu\mu\tau\tau$ would provide
a clear signal on top of the background in a di-muon invariant mass
distribution far from the $Z$ boson pole mass. The analysis is based on a
$\tau$-id algorithm which preselects events if they have two $\tau$ jets by
requiring a hadronic $\tau$ decay. Several benchmark points are defined for the
search, requiring a linear collider operating at $\sqrt{s} =$ 0.5 and 1 TeV. It
is shown that the signal can be observed on top of the background in all
benchmark points at an integrated luminosity of 1000 $fb^{-1}$.
