Question

If you cycle at a constant speed, does that mean there are no forces active?

Answer 1

If a body does not accelerate (or change direction) this means that the net force working on it is zero.

This does not mean there are no forces working on it. A book can be lying on my table, even though gravity is working on it. Its weight pushes in the table (a tiny bit) which as a reaction gives just enough spring force (reaction force) to counteract the gravity.

Compare it to a tug-of-war where both sides are equally strong. The flag won't move.

Same goes for objects moving at constant speed (and direction). If you cycle, you have to apply force on your pedals to counteract friction, air resistance etc. to keep up your (constant) speed.