O'Mara has agreed to a cameo in the ITV sitcom's fifth series but details of her character are being kept under wraps, The Sun reports.
O'Mara is best known for her role as Caress Morrell in Dynasty but her other credits include Doctor Who, Howard's Way and Bad Girls.
Other stars who have signed up for guest spots in Benidorm include Matthew Kelly and Michael Fenton Stevens, who has appeared in shows such as My Family, Pete Versus Life and Nighty Night.
Former Holby City star Siobhan Redmond and Phoenix Nights actor Ted Robbins will also appear in the comedy.
Loose Women's Sherrie Hewson joined the cast of Benidorm in August and will play the Solano's new manager Joyce Temple-Savage.
Benidorm is due to return on ITV1 later this month.