We present a molecular dynamics investigation of the electronic decoherence rate for electron transfer (ET) in a solvated protein molecule. We find that decoherence occurs on an ultrafast time scale of 2.4 fs, considerably faster than fluctuations in the electronic coupling. Both protein and solvent dynamics play important roles. Solvent alone would give rise to a decoherence time of 3.0 fs, as compared to 4.1 fs from the protein matrix alone. This implies that both solvation and protein dynamics can strongly affect both the rate and mechanism of ET.