  Inelastic neutron scattering experiments have been conducted to investigate
the semimetal system Yb$_3$Ir$_4$Ge$_{13}$. No clear crystal-field-split levels
were observed up to an excitation energy of 60 meV, while a magnetic excitation
appears at low energy below approximately 3 meV. This excitation shows a short
spatial correlation, and an energy spectrum is reproduced by an imaginary part
of generalized magnetic susceptibility on the basis of a damped harmonic
oscillator model. The magnetic excitation emerges simultaneously with an
anomalous electrical-resistivity enhancement below 20 K. The close relationship
between the magnetic and transport behaviors evidences that the semimetal
carriers are scattered by magnetic fluctuation dominated by the Yb $4f$ state.
