The new couple were recently spotted out together at the 25th annual KROQ Acoustic Christmas in LA last month, reported Us magazine.
"She loves to laugh. The past few girls haven't been fun enough for him, he's a child at heart," a source said.
Vandenberg, 28, has made guest appearances on TV shows such as 'Greek', 'Friends with Benefits', 'Go On', and 'For Better or Worse'.
She is currently filming the pilot for the new series 'Battle Creek' with Josh Duhamel.
Arnett, 44, was previously linked to celebrity chef Katie Lee and separated from Amy Poehler in September 2012 after nine years of marriage.