Lattice QCD with $N_c=2$ and $N_f=2$ is studied at imaginary
and real quark chemical potential $\mu_q$ at temperatures above $T_c$. We employ various methods of analytic continuation of the net baryon number $B$ from imaginary to real $\mu_q$. It is demonstrated that below the Roberge-Weiss temperature the cluster expansion model provides an accurate analytic continuation of $B$.