The characteristics of r.f. driven current are discussed. The results show thatonly for u=ω/(kxve)≤2-2.5 the current is carried by the resonant electrons and thedissipative mechanism is the resonant damping. When u≥3 the current will be carried by the non-resonant electrons and the dissipative mechanism will be collision damping. The dissipative power is usually much higher than the Ohmic power and the Lawson condition can be satisfied only for the case of u≤2-2.5. It is also shown that in a r.f. driven tokamak the poloidal rotation of plasma and the correspondent radial electric field are important.