The 40-year-old Underworld star wore a red and black floral mini-dress that highlighted her tiny waist and long legs. She complemented her look with earrings, strappy sandals and her long locks in a pony tail.
Beckinsale attended the event with husband Len Wiseman.
Other celebrity guests at the Warner afterparty were Chris Brown's on-and-off girlfriend Karrueche Tran, Taylor Swift's BFF Ed Sheeran, Bill Maher and former Desperate Housewives actress Andrea Bowen.
Jessica Simpson shares three-way kiss with friends in photo
Dennis Rodman pledges to end trips to North Korea