  Here we report the possible signature of Dirac fermions in the
magnetoresistance, Hall resistivity and magnetothermopower of LaAgSb$_2$. The
opposite sign between Hall resistivity and Seebeck coefficient indicates the
multiband effect. Electronic structure calculation reveals the existence of the
linear bands and the parabolic bands crossing the Fermi level. The large linear
magnetoresistance was attributed to the quantum limit of the possible Dirac
fermions or the breakdown of weak-field magnetotransport at the charge density
wave phase transition. Analysis of Hall resistivity using two-band model
reveals that Dirac holes which dominate the electronic transport have much
higher mobility and larger density than conventional electrons. Magnetic field
suppresses the apparent Hall carrier density, and also induces the sign change
of the Seebeck coefficient from negative to positive. These effects are
possibly attributed to the magnetic field suppression of the density of states
at the Fermi level originating from the quantum limit of the possible Dirac
holes.
