We present a measurement of the D-0 - (D) over bar (0) mixing parameter y(CP) using a flavor-untagged sample of D-0 -> (KSK+K-)-K-0 decays. The measurement is based on a 673 fb(-1) data sample recorded with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. Using a method based on measuring the mean decay time for different K+K- invariant mass intervals, we find y(CP) = (+0.11 +/- 0.61(stat.) +/- 0.52(syst.))%.