  The derivation of the nilpotent (anti-)BRST symmetries for the matter fields,
present in any arbitrary interacting gauge theory, has been an long-standing
problem in the framework of superfield approach to BRST formalism. These
nilpotent (anti-)BRST symmetries for the Dirac fields are derived in the
superfield formulation for the interacting Abelian gauge theory in four $(3 +
1)$-dimensions (4D) of spacetime. The same type of symmetries are deduced for
the 4D complex scalar fields having a gauge invariant interaction with the U(1)
gauge field. The above interacting theories are considered on the six $(4 +
2)$-dimensional supermanifold parametrized by four {\it even} spacetime
coordinates and a couple of {\it odd} elements of the Grassmann algebra. The
invariance of the conserved matter (super)currents and the horizontality
condition on the (super)manifolds play very important roles in the above
derivations. The geometrical origin and interpretation for all the above
off-shell nilpotent symmetries are provided in the framework of superfield
formalism.
