In this paper, we consider a special case of the general fractional plastic flow rule, namely the one which is equivalent to the classical non-associated Drucker-Prager (D-P) plasticity model. Fractional plastic flow is obtained from the classical flow rule by generalisation of the classical gradient of a plastic potential with a fractional gradient operator. It is important that, contrary to the classical models; non-associativity of fractional flow appears without introduction of the additional potential. The classical associative D-P plasticity is obtained as a special case. The discussion on objectivity of the fractional gradient is also presented also.