This article is from the Toyota RAV4 FAQ, by Ralph Becker with numerous contributions by others.
Yes, either or both seats can be removed. Here's how for a 2-door:
Each rear seat is held in place with 2 bolts. To remove, you have to
pop off 2 pieces of trim on each seat that cover the bolts. They are
at the front of the seat, about where a passenger's heels would be.
Then, remove the bolts with a socket wrench and a 14mm socket; a long
(6") extension is handy here. It may take a good deal of strength to
loosen these bolts. Finally, from the back, pull the seat release
loop and the seat should be free to pull out from the back.
Installation is the reverse; put the seat in place, line up the holes
in the seat brackets with the holes in the floor in the cabin, install
the bolts tightly, and snap on the bolt cover trim pieces. Installation
or removal should take just a few minutes.
The instructions are slightly different on a 4-door:
Each rear seat has a pair of angle brackets at the front of the seat.
Each angle bracket has two bolts. The bolts are very easy to get at,
provided one has an extender for the socket wrench. Remove them
and remove the seats as per the instructions for a 2-door.