reftex-no-include-regexps

reftex-no-include-regexps is a variable defined in `reftex-vars.el'.
Its value is

("\\.pstex_t\\'")

Documentation:
List of regular expressions to exclude certain input files from parsing.
If the name of a file included via \include or \input is matched by any
of the regular expressions in this list, that file is not parsed by RefTeX.

You can customize this variable.