This paper concerns the sensing of dynamic force/stress by means of a measuring system based on the use of an Fe-Ga sample (Galfenol) coupled to a magnetic circuit. The study is focused on the measurement of the effective magnetic field, detected at the rod specimen surface, and its variation DeltaHeff under time-dependent applied sinusoidal stress DeltaSigma oscillating at frequencies between 5 Hz and 20 Hz at different values of applied bias field Sigmabias (2.5 kA/m < Sigmabias < 27 kA/m). For the considered frequency and Hbias range, the measured DeltaHeff tends to linearly depend on DeltaSigma in contrast with the corresponding induction variation behavior (DeltaB - DeltaSigma), where hysteresis effects appear. With DeltaSigma in the range ± 15 MPa we obtain 0.06 MPa resolution in the determination of the alternating stress DeltaSigma, a result pointing to the effectiveness and sensitivity of this Galfenol-based method for detection and measurement of time-dependent stresses