The developed muscle activity imaging approach (MAI) was validated with surface EMG and intramuscular EMG signals simultaneously acquired from the biceps of a healthy male subject. 128 unipolar channels were employed for surface EMG measurement and one bipolar channel was employed for simultaneous intramuscular EMG measurement for the validation purpose. Ultrasound scans were also specifically performed to localize the location of the wire electrode inserted into the biceps. The surface EMG measurements, after noise filtering and signal decomposition, were used to reconstruct the internal muscle activities for the biceps by using the MAI approach. The locations of the reconstructed muscle activities were compared against the location of the wire electrode in the biceps identified from ultrasound images. Results demonstrate the feasibility and validity of the MAI approach in imaging internal muscle activities from multi-channel surface EMG recordings.