  We present the first observations of quiescent active regions (ARs) using
NuSTAR, a focusing hard X-ray telescope capable of studying faint solar
emission from high temperature and non-thermal sources. We analyze the first
directly imaged and spectrally resolved X-rays above 2~keV from non-flaring
ARs, observed near the west limb on 2014 November 1. The NuSTAR X-ray images
match bright features seen in extreme ultraviolet and soft X-rays. The NuSTAR
imaging spectroscopy is consistent with isothermal emission of temperatures
$3.1-4.4$~MK and emission measures $1-8\times 10^{46}$~cm$^{-3}$. We do not
observe emission above 5~MK but our short effective exposure times restrict the
spectral dynamic range. With few counts above 6~keV, we can place constraints
on the presence of an additional hotter component between 5 and 12~MK of $\sim
10^{46}$cm$^{-3}$ and $\sim 10^{43}$ cm$^{-3}$, respectively, at least an order
of magnitude stricter than previous limits. With longer duration observations
and a weakening solar cycle (resulting in an increased livetime), future NuSTAR
observations will have sensitivity to a wider range of temperatures as well as
possible non-thermal emission.
