I agree with the above, and assume you mean at a certain frequency.
Real values smaller than 1 simply mean the the supported mode is superluminal. This happens, for example, in solid metal waveguides just above cutoff. These frequency ranges generally aren't too useful, as it's difficult to match to those modes in that region. Metamaterials with these properties are used in planar form to create leaky-wave antennas.
Nonzero imaginary parts indicate loss if positive, but if negative suggest gain -- I would assume your material parameter extraction procedure is off here.