The finite temperature Casimir free energy is calculated for a dielectric ball of radius a embedded in an infinite medium. The condition ǫµ = 1 is assumed for the inside/outside regions. Both the Green function method and the mode summation method are considered, and found to be equivalent. For a dilute medium we find, assuming a simple "square" dispersion relation with an abrupt cutoff at imaginary frequencyω = ω0, the high temperature Casimir free energy to be negative and proportional to x0 ≡ ω0a. Also, a physically more realistic dispersion relation involving spatial dispersion is considered, and is shown to lead to comparable results.