Yes, zombies of that type get an immediate activation. Do not discard that card and draw another, do whatever is on the card. Nothing will spawn in room/zone of the corresponding "special" card. This is covered in the first page of the FAQ
Q: When spawning the Zones of a building I just opened, what happens if I draw an extra activation or manhole card?
A: Always do exactly what the card says no matter when you draw it. If you draw an extra activation card, that Zombie type receives an extra activation immediately. If tou draw a manhole card, spawn Zombies in the manholes normally. in these cases, the building Zone for which the card was originally drawn receives no Zombies.
This is also repeated at the bottom of page 10 of the rule book, just above the so many zombies, so few miniatures sidebar.
There are two special cases: the “extra activation” cards and the “manhole” cards. In both cases, no Zombies appear on the designated Zone.