The actress said that fans can never be sure if and when her character Jean Grey could return.
"One never knows," she told MTV News. "Jean Grey, the Phoenix... she finds a way to reincarnate herself constantly, so one never knows."
The actress added that she is "in no position to say anything" about specific plans for Grey to return to the big screen.
"I have no idea," she said. "Stay tuned."
Janssen starred in the X-Men trilogy alongside Patrick Stewart, Ian McKellen and Hugh Jackman.
She will next star in Taken 2 - which will debut later in the week - and recently made her directorial debut on Bringing Up Bobby.
Stewart recently suggested that he would return to the role of Professor Charles Xavier in X-Men: Days of Future Past.