Chatter is one of the major barriers for robotic machining process. As the dominant vibration frequency of the chatter varies under different working conditions, Magnetorheological elastomers (MREs) whose stiffness is adjustable is an ideal device to be used for chatter control. This paper presents a new mode coupling chatter reduction scheme by assembling an MRE absorber on the spindle to absorb vibration with a specific frequency range. Firstly, a MRE absorber was designed and fabricated to suppress the target chatter according to the robot model and then a test was implemented to obtain the frequency shift property of the designed MRE absorber. Subsequently, robotic milling of an aluminium block using ABB IRB6660 robot was tested under various conditions to demonstrate the performance of the MRE absorber under different constant currents. After that, a semi-active controller was established to control the electrical current applied to the MRE absorber to trace the chatter frequency. The experimental results show that the semi-active MRE absorber performs better on the chatter reduction during robotic milling than passive absorbers.