We present a detailed study of the stellar kinematics in the barred galaxy NGC 5728 based on I-band photometry and long-slit spectroscopic observations in the region of the near-IR Ca II triplet. The analysis of the stellar line-of-sight velocity distribution (LOSVD) has revealed, in the central regions of the bar, the presence of a cold (v/sigma~2.5), prograde, S-shaped velocity component that coexists in the central 4 kpc, with a fainter and hotter (v/sigma~0.5) counterrotating component. Beyond 4 kpc from the nucleus, the LOSVD shows the stellar bar kinematics. The comparison of the radial surface brightness profile of the velocity components with that obtained from an I-band image shows that the counterrotating core follows a r^1/4 profile, while the S-shaped component does not follow the flat-bar surface brightness profile. Several possible scenarios accounting for such kinematic signatures found in the center of the bar in NGC 5728 are discussed. The data presented in this paper show for the first time the presence of extended retrograde motions in barred systems that, together with previous discoveries, seem to indicate that the stellar counterrotation is a phenomenon present all along the Hubble sequence.