The destruction or the use of your computer? Regarding the former, unfortunately, that is true, as many of the beldum line’s powers stem from magnetism. The more excited and the further down the evolutionary line an individual is, the more likely it will release a magnetic burst that can interfere quite badly with computers. On the other hand, the further up the evolutionary line an individual is, the better control over itself it will have, so a metagross might be able to exercise enough self-restraint to avoid frying anything it comes in contact with.
Of course, this covers magnetic damage; it doesn’t cover physical. On that note, if you find that your keyboard is strangely worn or even completely destroyed by what seems to be a set of heavy claws … then yes, your metagross has been using your computer. If not, then you’re probably all right.