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