  Guo, Alexandradinata, \textit{et al.} have recently proposed that
quantum-oscillation frequencies from Dirac/Weyl fermions exhibit a negative
shift proportional to $T^2$ because of the energy dependence of the effective
mass peculiar to a linear band-dispersion. We have measured Shubnikov--de Haas
oscillation in CaFeAsF up to $T$ = 9 K. The frequency of the $\alpha$ Dirac
electron exhibits a negative shift with increasing $T$, while that of the
$\beta$ Schr\"odinger hole does not. For $T \geqslant 5$ K where $\beta$ is
negligible, the $\alpha$-frequency shift is proportional to $T^2$ and its rate
agrees with the theoretical prediction within experimental accuracy. At lower
temperatures, the shifts of $\alpha$ and $\beta$ deviate from theoretical
expectations, which we ascribe to the inaccuracy in the frequency determination
due to unfavorable interference between frequencies. Our results confirm that
the topological frequency shift can be utilized to identify Dirac/Weyl fermions
when quantum-oscillation frequencies can be determined accurately.
