12/09/2013 at 04:15 PM EST
On Saturday, Kerry Washington
attended film and television producer Jennifer Klein's annual holiday party in Los Angeles.
Wearing a black, fitted dress with her hair pulled back the Scandal
actress arrived around 10 p.m. at the Evian sponsored event with her costars, Scott Foley
and Katie Lowes
The expectant mother
– who sipped water during the event – was "definitely in a very upbeat, celebratory mood throughout the whole evening," an onlooker tells PEOPLE.
Other guests at the soiree included Lily Collins
, Gal Gadot
– who was recently cast as Wonder Woman –, Tyra Banks, Topher Grace, The Best Man Holiday
's Sanaa Lathan and James Marsden among others.
– Jennifer Garcia