An actively mode-locked optoelectronic oscillator (OEO) scheme was proposed to generate high-repetition-rate microwave pulse signals based on high-order harmonic mode locking. In the proposed scheme, the bias port of the electro-optic intensity modulator in the cavity was driven by a sinusoidal signal. The frequency of the sinusoidal signal ( ${f_{bias}}$) was set to be $N$ times of the free spectral range of the OEO cavity to realize fundamental ( $N = 1$) and harmonic ( $N \geqslant 2$) mode locking, where the repetition rate of the generated microwave pulse signal was equal to ${f_{bias}}$. In the proof-of-concept experiment, 10th-, 50th- and 100th-order harmonic mode locking were realized, where the repetition rate of the generated microwave pulse signal was 360 kHz, 1.8 MHz and 3.6 MHz, respectively. The proposed actively mode-locked OEO scheme provides a new way to generate low-phase-noise microwave pulse signals for pulse Doppler radar application.