  An analysis is given of the Belle II sensitivities and NA64 constraints on
the sub-GeV Dirac dark matter that interacts with charged leptons. We consider
two different types of interactions between sub-GeV Dirac dark matter and the
charged leptons: the EFT operators and the light vector mediators. We compute
the Belle II mono-photon sensitivities on sub-GeV dark matter with 50 ab$^{-1}$
data which are expected to be accumulated in the full Belle II runs. Although
the Belle II mono-photon sensitivities on the EFT operators are of similar size
as the LEP constraints, Belle II can probe new parameter space of the light
vector mediator models that are unexplored by LEP. For both the EFT operators
and the light vector mediator models, the Belle II mono-photon sensitivities
can be several orders of magnitude stronger than the current dark matter direct
detection limits, as well as the white dwarf limits. The light vector mediator
can also be directly searched for by reconstructing the invariant mass of its
di-lepton decay final states at Belle II, which is found to be complementary to
the mono-photon channel. We compute the NA64 constraints on the sub-GeV Dirac
dark matter and provide analytic expressions of the dark matter cross section
in the Weizs\"acker-Williams approximation, for the EFT operators, and for the
light vector mediator models. We find that the current NA64 data (with $2.84
\times 10^{11}$ electron-on-target events) provide strong constraints on
sub-GeV dark matter. Although the NA64 constraints are found to be about one
order of magnitude smaller than the Belle II sensitivities for the EFT
operators, NA64 can probe some regions of the parameter space in the light
vector mediator models that are beyond the reach of Belle II.
