A novel haptic interface for musical keyboards is presented. The piano key has an embedded active damping system based on magneto-rheological (MR) fluids that allows to reproduce the dynamic behavior of traditional pianos. The MR fluid is encapsulated into a mechanical sealing to avoid leakage. A slider is attached to the back of the key and shears the MR fluid. When a magnetic field is applied across the MR fluid, chains of particles are aligned along the magnetic field lines. The strain of the chains will create a resistant force that can be controlled on real time. An analytical model of the whole system is presented and compared to experimental results.