We investigate collective excitations in quark-gluon plasma at high temperatures. Ultrarelativistic plasmas are of importance in cosmology, astrophysics, and high energy nucleus-nucleus collisions. One of the fundamental properties of a thermal field theory at finite temperatures is the collective excitations, which are characterized by dispersion law omega(p) giving their energy as a function of their momenta p. Collective modes appear mathematically as poles of propagators with well-defined quantum numbers in the complex plane of the energy: the real part of the pole gives the dispersion law, while the imaginary part gives the damping rate. In this paper, Bose excitations in quark-gluon plasma are investigated in the lightcone gauge. In order to remove non-physical singularities, which appear in non-covariant gauges in non-abelian gauge field theories, we used the Mandelstam-Leibbrandt prescription. Gluon self-energy in the one-loop approximation is calculated using standard Thermal QCD diagram technique. Bose excitation spectrum is found in the high-temperature limit and the dispersion equation is shown to be gauge invariant.