In Xmen are there any other level 5 mutants other than Jean Gray?

Level 5 is a classification that only came about from the X-men movies, and was only used in "X-men: The Last Stand". In the comic books, they classify the level of mutant's powers a bit differently. They used to use a three part classification system, but it has recently been extended to a seven part system, which will be explained a bit farther down.

It has been said by the director that they changed the movie system from the comic's because they thought it would be easier for people to understand. Numbers tend to be easier to immediately comprehend instead of telling people an obscure word and having them understand. Level 1 instead of delta and level 5 instead of omega.

The comics system used to go by three levels of power : beta, alpha, and omega. However, this didn't prove to be a broad enough scale, so they had to add to it. Recently, this was expanded to a seven part system : zeta, epsilon, delta, gamma, beta, alpha, and omega. If we were to connect the two scales, it would look something like this.

"Normal" or Human = non-mutant humans and zeta level mutants

Level 1 = Epsilon

Level 2 = Delta

Level 3 = Gamma and Beta

Level 4 = Alpha

Level 5 = Omega

In the comics, there are several "Omega-level" mutants, some of whom are : Jean Grey, Robert Drake, Emma Frost, Gabriel Summers, Nate Grey, and Franklin Richards, among others.

The only mutant in the films stated to be that powerful is Jean Grey. However, especially in recent movies, Magneto has shown significant displays of power. Also, in the upcoming "X-men: Apocalypse", Apocalypse may be a class five mutant as well, if it follows comic canon. Until it is stated as such on screen, Jean Grey will remain the ONLY class five mutant.