In this paper, convergence and performance properties of a sample-data continuous time model predictive control (MPC) scheme with economic performance index are developed. In particular, we provide sufficient conditions for convergence of the close loop state trajectory to a steady state and constructive methods to design a terminal set and a terminal cost to satisfy them. Further, considering an average performance index, sufficient conditions under which the system in closed loop with the MPC controller outperforms the system operated at the economically optimal steady state are derived for the case of convergent and non convergent behaviors. Two numerical examples are presented to illustrate the different design techniques.