That depends on the technique. In research, meditation techniques are often divided into two broad groups: Focused Attention Meditation (FAM) and Open Monitoring Meditation (OMM). FAM techniques require meditators to direct their attention to a particular object and keep it there. This might involve observing the breath, other physical sensations, a mantra, or other objects of thought or imagination.
To keep attention there, you have to continually monitor both your own attention and distracting thoughts (metacognition).
In OMM, by contrast, the focus is on observing mental activity itself without intervening in it. The meditator notices which thoughts, feelings, impulses, motivations, perceptions, and so on arise from moment to moment, how they change, and how they disappear again. OMM is often regarded as a more advanced technique than FAM.1