Nouns ending in -té are usually feminine.
The suffix marks an abstract quality.
Is activité masculine or feminine?
l'activité
The rule behind it
91.3% of -té nouns are feminine
In context
Mes activités officielles me prennent beaucoup de temps.
My public duties take a lot of time.
Nous terminons ainsi les activités d'aujourd'hui.
And with that we finish the activities for today.
Elle prend part à beaucoup d'activités scolaires.
She participates in many school activities.