Magneto's suit is made of flexible metal bonded on the molecular level, providing protection against projectiles, energy weapons, and concussive force. His helmet, which is built out of the same metal as Charles Xaviers "Cerebro", allows him to keep telepathic attack from harming him and also shields his mind from "Cerebro". http://en.wikipedia.org/wiki/Magneto_(comics)

Wikipedia is not always right. I know, *gasp*! I've been reading X-Men for a long time and I'm pretty sure that's not right. The reason Xavier hasn't invaded Magneto's mind often is because they were very close friends and Xavier still has a great deal of respect for him. Plus the last time Xavier invaded his mind, Onslaught was born. Juggernaut is the one who has a helmet that blocks telepathy.

No. Despite the fan confusion created by the film and the Ultimate Universe, but Magento's helmet has never protected him from psychic attacks in the 616 (mainstream Marvel continuity). Back in the Silver Age Magneto installed tech in the helmet to control mens' minds, and that was briefly resurrected in the X-Men vs. Avengers miniseries of the 1980's, but there is simply zero evidence indicate that it blocks telepathy. He has had his helmet knocked in the presence of telepaths many times before (in fact I'm hard pressed to remember a single fight he has been in since the Silver Age in which the helmet was *not* knocked off), and he has expressed no concern. (Which brings up the fact that why would anyone put their trust in a defense so easily removed?) In fact, in X-Men Vol. 2 #25 (Fatal Attractions) without his helmet, it took the combined might of both Xavier and Jean Grey to make a crack in Magneto telepathically. Ever since the Silver Age Magneto has always had a limited telepathic ability. He had to, or he would have been too easily defeated by Xavier. This continued through the 1980's and 1990's. Without his helmet, Magneto has been able to resist telepathic attack (noted above), project his astral form (Marvel Fanfare #33, X-men vs. Avengers miniseries), and be sensitive enough to pick up on others feelings (New Mutants Vol. 1 #38). In Secret Wars I, Jim Shooter attributed it to "latent telepathy", but Chris Claremont attributed it to the character's iron will and mental discipline, much like Dr. Strange has all of these abilities without being a telepath. Recently fans have suggested that because the brain transmits signals from neuron to neuron with bioelectricty, Magneto's power can mimic certain aspects of telepathy (though he is not nearly as adept as a someone who brain is specifically adapted for it as Charles is) and in case of telepathic assault, he can maintain his "operational integrity".

It keeps them from reading his thoughts but not against psychic attacks I think Juggernaut however his mystic helmet does protect him from psychic attacks