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abstract: 'We conducted a high resolution mid-infrared spectroscopic investigation using [*Spitzer*]{} of 32 late-type (Sbc or later) galaxies that show no definitive signatures of Active Galactic Nuclei (AGN) in their optical spectra in order to search for low luminosity and/or embedded AGN. These observations reveal the presence of the high ionization \[NeV\] 14$\mu$m and/or 24$\mu$m line in 7 sources, providing strong evidence for AGNs in these galaxies. Taking into account the variable sensitivity of our observations, we find that the AGN detection rate based on mid-infrared diagnostics in optically normal late-type galaxies is $\sim$ 30%, implying an AGN detection rate in late-type galaxies that is possibly 4 times larger than what optical spectroscopic observations alone suggest. We demonstrate using photoionization models with both an input AGN and an extreme EUV-bright starburst ionizing radiation field that the observed mid-infrared line ratios in our 7 AGN candidates cannot be replicated unless an AGN contribution, in some cases as little as 10% of the total galaxy luminosity, is included. These models show that when the fraction of the total luminosity due to the AGN is low, optical diagnostics are insensitive to the presence of the AGN. In this regime of parameter space, 