The Emmy Award-winning series, set in the early 20th century, follows the lives of a wealthy British family and the loyal employees who serve them in their country mansion. Smith plays the family's formidable matriarch.
The show, now shooting its third season, airs on ITV in the United Kingdom and on PBS in the United States.
A widely cited newspaper report said Smith had asked the show's creator, Julian Fellowes, to write her character out after Season 3 ends because she is eager to focus on theater and film projects.
However, a representative for Carnival Film and Television Limited, co-producers of the series, told the Vancouver Sun Monday: "Series 3 is currently filming with Maggie along with the other cast. We do not comment on future story lines, however there is no truth in the story that Maggie is leaving the show."
Smith, 77, won an Oscar for her work in the 1969 film "The Prime of Miss Jean Brodie." She starred in the 2002 Best Picture Oscar winner "Gosford Park," which Fellowes wrote, and appeared in all of the Harry Potter blockbusters.