High-power　mid-infrared　2.8-mu　m　ultrafast　laser　has　potential　applications　in　the　fields　of　laser　surgery　due　to　its　wavelength　overlap　with　the　absorption　peak　of　water.　In　this　work,　we　demonstrate　a　2.8-mu　m　picosecond　Raman　laser　in　a　methane-filled　hollow-core　anti-resonant　fiber　(HC-ARF)　with　average　power　of　4　W,　pulse　energy　of　40　mu　J,　and　beam　quality　of　1.47.　The　laser　beam　quality　improvement　at　mid-infrared　Raman　conversion　in　methane-filled　HC-ARF　is　firstly　observed.　This　work　heralds　a　promising　approach　to　generate　mid-infrared　ultrafast　Raman　laser　with　multi-Watt　level　average　power　and　high　beam　quality.