  We report the serendipitous discovery of a group or cluster of young galaxies
at $z\simeq$2.40 in a 24-orbit HST/WFPC2 exposure of the field around the weak
radio galaxy 53W002. Potential cluster members were identified on ground-based
narrow-band redshifted Ly$\alpha$ images and confirmed via spectroscopy.
  In addition to the known weak radio galaxy 53W002 at z=2.390, two other
objects were found to have excess narrow-band Ly$\alpha$ emission at
$z\simeq$2.40. Both have been spectroscopically confirmed, and one clearly
contains a weak AGN. They are located within one arcminute of 53W002, or
$\sim0.23h_{100}^{-1}$Mpc ($q_o$=0.5) at $z\simeq$2.40, which is the physical
scale of a group or small cluster of galaxies. Profile fitting of the WFPC2
images shows that the objects are very compact, with scale lengths
$\simeq$0\farcs 1 ($\simeq0.39h_{100}^{-1}$kpc), and are rather faint
(luminosities < L*), implying that they may be sub-galactic sized objects. We
discuss these results in the context of galaxy and cluster evolution and the
role that weak AGN may play in the formation of young galaxies.
