It happens a lot in speech and in fact happened to me an hour ago. I was talking to a friend and I had to say the word "relevant" but instead I said "revelant". "It is not revelant". That obviously makes sense but the word has its sounds interchanged. Is there a term (technical or ordinary) for such kind of mistakes?
Linguists call it metathesis. For example, “bird” is a mispronunciation of “bridd.” Here is another example.
A more extreme version is sometimes called a “malapropism” after a character named “Mrs. Malaprop” in a 1775 comedy, who constantly said things like “The queer old Dean” instead of “The dear old Queen.”
If you're specifically asking for an English word that describes this phenomenon (where it is a simple mistake and not a more serious disorder), I don't think there is one that describes it exactly.
You can call it a flub, although this word is most commonly used in acting; the phrase "to flub one's line" means to say a line incorrectly . It covers the case where you're describing, but it's broader than that, and includes any kind of speaking mistake such as when you mix up word order or say an entirely different word altogether.