Yes, EXTRANEOUS is a Scrabble word!

Letter values in Scrabble US: E 1, X 8, T 1, R 1, A 1, N 1, E 1, O 1, U 1, S 1.

Is it a valid word?

EXTRANEOUS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

not pertinent to the matter under consideration
not essential
not belonging to that in which it is contained; introduced from an outside source
coming from the outside