  Chemically non-equilibrated quark-antiquark matter is studied within the
Nambu-Jona-Lasinio model. The equations of state of non-strange (q=u,d) and
strange (q=s) quark-antiquark systems are calculated in the mean-field
approximation. The existence of metastable bound states with zero pressure is
predicted at finite densities and temperatures less than about 50 MeV. It is
shown that the minimum energy per particle occurs for symmetric systems, with
equal densities of quarks and antiquarks. At T=0 these metastable states have
quark number densities of about 0.5 fm^-3 for q=u,d and of 1 fm^-3 for q=s. A
first order chiral phase transition is found at finite densities and
temperatures. The critical temperature for this phase transition is
approximately 75 MeV (90 MeV) for the non-strange (strange) baryon-free
quark-antiquark matter. For realistic choices of parameters, the model does not
predict the phase transition in chemically equilibrated systems. Possible decay
channels of the metastable quark-antiquark droplets and their signatures in
relativistic heavy-ion collisions are discussed.
