In this paper we will analyse the ABJM theory in harmonic superspace. The
harmonic superspace variables will be parameterized by the coset SU(2)/U(1)
and thus will have manifest N=3 supersymmetry. We will study the
quantum gauge transformations and the BRST transformations of this theory in
gaugeon formalism. We will use this BRST symmetry to project out the physical
sub-space from the total Hilbert space. We will also show that the evolution of
the S-matrix is unitary for this ABJM theory in harmonic
superspace.Comment: 11, pages, 0 figures, accepted for publication in Mod. Phys. Lett.