The actress, who plays Juliet Burke, was last seen in the season five finale trying to explode a hydrogen bomb with a rock as the end credits flashed to white.
ABC hinted that Mitchell will be back in the drama, as well as the recently greenlit update of cult sci-fi show V, according to TV Guide.
"We're thrilled to be able to have her do both [shows]," said ABC entertainment president Stephen McPherson. "It was a little bit of a juggling act... and we're very thankful to the [accommodating Lost] producers, but I think we'll see her on Lost during the show's final season."
V, which will be a midseason replacement, stars Mitchell as a Homeland Security agent who does battle with lizard-like alien beings.