Oh yes. If you are using a typical home router then you can use:
* Passwords / Passphrases
* MAC address filters (Not the most effective but it is just an extra layer of security)
* Hide broadcasting your wireless signal
* Create a guest-wifi to isolate guests from you
* Lower the power of your wifi signal so people down the road can't pick up on the signal as easy
I will add more things if I think of more.
To help you sleep well at night: If someone wants to access your wireless network. It will happen by any semi-intelligent geek. It is a trivial achievement to hack wifi even with the highest encryption. If security is important then ensure the data is transferred over a wire. Not through the air we breath.
I HIGHLY suggest using a pass phrase with unique characters ($, ü, 2, E, e, 123)
Example: Toto was a fast boy 1@