As of my limited knowledge up until September 2021, there are no known comets on a collision course with Mars. The latest comet to catch the attention of astronomers in relation to Mars was Comet C/2013 A1 Siding Spring, which passed the red planet in October 2014. However, the closest approach was still several thousand miles away, and the comet did not pose any threat to Mars or its moons.

Cometary trajectories can be quite unpredictable, so it's always possible for a new comet to be discovered that could pose a risk to Mars in the future. However, currently, there are no known comets on a collision course with the red planet.

To get the most up-to-date information on any potential cometary threats, I recommend checking with a reliable source, such as NASA or the European Space Agency.