The winner will be announced during the 2016 NHL Awards on June 22 at the Hard Rock Hotel & Casino in Las Vegas.
Kopitar also is a finalist for the Selke Trophy, awarded to the League's top defensive forward.
In 81 games this season, Kopitar led the Kings with 74 points and was second in the League with a plus-34 rating (teammate Tyler Toffoli was plus-35). He had 16 penalty minutes averaging 20:52 of ice time per game.
Kopitar finished third in Lady Byng voting last season. The last Kings player to win the Lady Byng was Wayne Gretzky in 1994.
Barkov had NHL career-bests this season in goals (28), assists (31) and points (59), and had eight penalty minutes in 66 games. He is the first Panthers player to be a Lady Byng finalist since defenseman Brian Campbell won the award in 2012.
Eriksson is a Lady Byng finalist for the second time; he was third in voting in 2011. This season he had 30 goals and 63 points, and 12 penalty minutes in 82 games. The last Bruins player to win the Lady Byng was Rick Middleton in 1982.
Jiri Hudler of the Calgary Flames won the award last season.