  We report positive muon spin relaxation measurements on the triangular
lattice magnetic system FeGa2S4. A magnetic transition not previously detected
by specific heat and magnetic susceptibility measurements is found in zero
field at T^* \simeq 30 K. It is observed through the temperature dependencies
of the signal amplitude and the spin-lattice relaxation rate. This transition
is therefore not a conventional magnetic phase transition. Since persistent
spin dynamics is observed down to 0.1 K, the ground state cannot be of the
canonical spin-glass type, which could be suggested from hysteresis effects in
the bulk susceptibility below T_f \simeq 16 K. These results are compared to
those found for the isomorph NiGa2S4. It is argued that the fate of the
transition, which has been interpreted in terms of the Z_2 topological
transition in this latter system, is probably different in FeGa2S4.
