Currently it is not possible to use \overarc with <math>. But it seems \overarc is a standard LaTeX symbol. So no idea if the problem comes from AMS-LaTeX or elsewhere.
An acceptable workaround for the moment is to use \overset{\frown}{AB} instead.
PS and off-topic: It took me some time to find out this "Math (texvc)" component in this product. I was looking for AMS-LaTeX in other product.
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Possible Solution:
/overarc is currently not listed in the "math" extensions list about available macros.
The consent from the discussion about this topic seems to be to implement the /overarc function using the ⏜ character.
This can be done by adding /overarch to the list of available macros and then implementing it the same way as e.g. /overbracket just with the 23DC character instead of 23DE.
The current workaround uses a <span> element, creating a cruved line as text decoration in html. While this looks more acurate it cannot be easily replicated with the use of unicode characters in a <math> element. Therefore I would suggest the approach mentioned above.
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**Version**: unspecified
**Severity**: normal
**See Also**:
https://github.com/mathjax/MathJax/issues/567