Yes, ACTION is a Scrabble word!

Letter values in Scrabble US: A 1, C 3, T 1, I 1, O 1, N 1.

Is it a valid word?

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

something done (usually as opposed to something said)
the state of being active
a military engagement
a process existing in or produced by nature (rather than by the intent of human beings)
the series of events that form a plot
the trait of being active and energetic and forceful
the operating part that transmits power to a mechanism
a judicial proceeding brought by one party against another; one party prosecutes another for a wrong done or for protection of a right or for prevention of a wrong
an act by a government body or supranational organization
the most important or interesting work or activity in a specific area or field

Also: military action, natural process, natural action, action mechanism, legal action, action at law, carry through, carry out.