  Mid-infrared observations are powerful in identifying heavily obscured Active
Galactic Nuclei (AGN) which have weak emission in other wavelengths. Data from
the Mid-Infrared Instrument (MIRI) onboard JWST provides an excellent
opportunity to perform such studies. We take advantage of the MIRI imaging data
from the Cosmic Evolution Early Release Science Survey (CEERS) to investigate
the AGN population in the distant universe. We estimate the source properties
of MIRI-selected objects by utilizing spectral energy distribution (SED)
modelling, and classify them into star-forming galaxies (SF), SF-AGN mixed
objects, and AGN. The source numbers of these types are 418, 111, and 31,
respectively, from 4 MIRI pointings covering $\sim 9$ arcmin$^2$. The sample
spans a redshift range of $\approx 0$--5. We derive the median SEDs for all
three source types, respectively, and publicly release them. The median MIRI
SED of AGN is similar to the typical SEDs of hot dust-obscured galaxies and
Seyfert 2s, for which the mid-IR SEDs are dominantly from AGN-heated hot dust.
Based on our SED-fit results, we estimate the black-hole accretion density
(BHAD; i.e., total BH growth rate per comoving volume) as a function of
redshift. At $z<3$, the resulting BHAD agrees with the X-ray measurements in
general. At $z>3$, we identify a total of 27 AGN and SF-AGN mixed objects,
leading to that our high-$z$ BHAD is substantially higher than the X-ray
results ($\sim 0.5$ dex at $z \approx 3$--5). This difference indicates MIRI
can identify a large population of heavily obscured AGN missed by X-ray surveys
at high redshifts.
