Both wideouts will be on a “rep count,” a source told ESPN’s Adam Schefter.
Williams previously was not expected to play because of a back injury, while the Chargers had been concerned they could be without Allen because of a hamstring issue.
Chargers running back Austin Ekeler (quad) also is active after being listed as questionable.
Allen is second in the NFL this season with 99 receptions and leads the Chargers with 975 yards and eight touchdown receptions. Williams is second on the team with 572 receiving yards and has 36 receptions and four touchdowns.
Ekeler is the Chargers’ rushing leader with 407 yards and third on the team with 41 receptions.
The Chargers, who beat the Atlanta Falcons on Sunday to snap a two-game losing streak, are in last place in the AFC West this season with a 4-9 record.