The pair went to watch the Los Angeles Lakers holiday game against the New York Knicks in downtown Los Angeles where they were pictured cuddling up together courtside, whispering in each others ear and sharing jokes.
According to gossip website TMZ.com they arrived together in the same car but entered the Staples Centre separately.
Rihanna and Chris later posted a picture of themselves online posing in front of a car, with the caption "Thuglife".
The couple split in 2009 after Chris was arrested for assaulting Rihanna the night before the Grammy Awards. They have since caused controversy by rekindling their friendship, and while they have been spotted sharing many intimate moments together in recent months, Rihanna tweeted last week that "being single sucks".
And The Sun reported Rihanna has a rival for Chris' affections.
She also posted a picture of herself in lingerie blowing a kiss to Chris with the message, "Merry Christmas baby". In return he "liked" the photo.