Harrison wore a black suit and white dress shirt to the event while Zima wore a red jumpsuit.
Harrison, 47, and Zima, 31, have been "dating for months and are very happy, according to ET.
Zima later posted a photo of the couple posing on the red carpet on her Instagram account, captioning it with only a red heart emoji.
Zima joined Entertainment Tonight in 2015 and serves as the entertainment news outlet's reporter for all things Bachelor-related.
Her coverage includes hosting The Bachelor: Roses and Rose, a recap show that is available on Entertainment Tonight's Youtube Channel.
Prior to joining Entertainment Tonight, Zima worked for the news network Newsy.
In early December, Zima had posted a photo of herself and Harrison posing with a promotional poster for Colton Underwood's season of The Bachelor and captioned it "the two most important men in my life, TBH."
Harrison and his former wife Gwen divorced in 2012 after 18 years of marriage.
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"Though we have made this incredibly difficult decision to separate, our love and mutual respect remain, and we look forward to sharing in the lives of our wonderful children," the couple said in a statement at the time.