A Z2Z4-additive code C subset of Z_2^alpha x Z_4^beta is called cyclic if the set of coordinates can be partitioned into two subsets, the set of Z_2 and the set of Z_4 coordinates, such that any cyclic shift of the coordinates of both subsets leaves the code invariant. Let Phi(C) be the binary Gray image of C. We study the rank and the dimension of the kernel of a Z2Z4-additive cyclic code C, that is, the dimensions of the binary linear codes <Phi(C)> and ker(Phi(C)). We give upper and lower bounds for these parameters. It is known that the codes <Phi(C)> and ker(Phi(C)) are binary images of Z2Z4-additive codes R(C) and K(C), respectively. Moreover, we show that R(C) and K(C) are also cyclic and we determine the generator polynomials of these codes in terms of the generator polynomials of the code C.