I have a chihuahua terrier mix 4 weeks old,will the ears stand up?

There is absolutely no way for us to say. You haven't mentioned what sort of terrier or provided any sort of picture, the puppy is only 4 weeks and not all Chihuahuas ears will stand. The first link is the Chihuahua parent club and you can look up terrier breed clubs in the second link.
http://www.chihuahuaclubofamerica.com/ http://www.akc.org/breederinfo/breeder_search.cfm
q5762034.html#a2906893 http://www.wildheirlabradorrescue.org/readingroom/what-is-a-back-yard-breeder.php 
http://members.tripod.com/antique_fcr/goodbreeder.html 
http://www.wonderpuppy.net/1breeding.php
http://home.comcast.net/~NoPuppyMillsVA/Poo-dogs___Designer_Mutts/poo-dogs___designer_mutts.html
http://www.petfinder.com/index.html