First off, as Sutek pointed out, the TWF penalties are different in Conan.
- No TWF feat and off-hand weapon is one-handed: -6/-6
- No TWF feat and off-hand weapon is light: -2/-2
- TWF feat and off-hand weapon is one-handed: -4/-4
- TWF feat and off-hand weapon is light: -0/-0
Now, to answer your origional question: yes, many classes get the Two Weapon Fighting feat for free. This is listed in a strange place, under the class weapon and armor proficiencies. Those classes which are proficient with "two weapon combat" get the Two Weapon Fighting feat for free. Why did they put it under the weapon proficiencies? Who knows? I suspect at one time they may have been playing around with renaming the feat chain "Weapon Proficiency [two weapon combat]" but that is just a guess.
Now, as to you question "is this overpowering"? The answer is no, not really. Almost all the classes get TWF for free in Conan. IIRC the only ones who don't are the Scholar and the Thief (classes with less of an emphasis on combat). Since everybody gets it everybody is on equal footing, much the same way that everybody in Conan can Finesse without requiring a feat or Fight on the Run without requiring a feat. It simply means that, in this respect, Conan characters are more capable than basic dnd characters. If you are trying to mix Conan classes with classes from other sources then this becomes an issue, but in that case you already have a lot of re-balancing to do anyway.
What this means is that Conan characters are more versatile than you are used to. TWF is good for dealing with hordes of lightly-armored mooks, THF is good for dealing with single big foes. A character should change his style to fit his opponent and the Conan rules support this.
Hope that helps.