We present a new method based on mid-IR (5 — 16 µm) emission for classifying the origin of the mid-IR activity in galaxies. Our method was devefoped using a set of 33 ISOCAM spectra of extragalactic sources which exhibit diverse mid-IR spectral features. Detailed analysis of our sample enables us to identify the general properties of mid-IR emission from active galactic nuclei (AGNs), starbursts, and quiescent star forming regions. The benefits of this mid-IR classification for identifying obscured or faint AGNs and for estimating the star formation intensity in star-forming regions are investigated.