Don't worry, this is normal behavior to remove the dried "velvet" from the antlers.

This special skin (velvet) is critical for supporting the explosive growth of the antlers...

Antlers exhibit the fastest bone growth among vertebrates, and to support this high growth rate, these structures are richly supplied with blood (and therefore nutrients and oxygen) through branches of the superficial temporal artery.

The extremely high growth rate of antlers can reach 2.75 cm/day and reach 15 kg in mass and 120 cm in length in just ~3 months. In moose, the antlers can weigh up to 30 kg!

In general, deer antlers are regenerated annually in the spring, when the hardened structure is lost, and then grow rapidly in the summer and undergo ossification in the autumn, after which the covering skin (velvet) is removed.

The growth cycles of antlers are controlled by androgens and immune factors, particularly macrophages.

And don't confuse antlers with horns. Horns in mammals are keratinous structures that surround a bony core and are permanent (they don't fall off and regenerate periodically). Bovids, for example, have horns.