Tell me some free antivirus for my nokia n72

there is some virus in my mobile

Most anti-virus producers will let you download atrial version for free. However, if what you mean is where you candownload a free anti-virus product for your phone. But for the good ones you have topay. See below for links to download pages.
http://www.avira.com/en/download/downloa...
http://www.bitdefender.com/site/Main/vie...
http://www.symbian-freak.com/news/006/04...
http://www.exosyphen.com/page_exovirusst...
http://www.f-secure.com/partners/mobile_...
http://www.fonoinfo.com/downlaod_command...
http://www.fortiguardcenter.com/mobile/t...
http://www.kaspersky.com/trials?chapter=...
http://mobile.mcafee.com/(osoogm55x2yzlo...
http://www.mpulze.com/antivirus.php?part...
http://www.netqin.com/english/download.h...
http://updates.pandasoftware.com/beta/Mo...
http://www.simworks.biz/sav/AntiVirus.ph...
http://www.smobilesystems.com/ota/shoppi...
http://www.umuglobal.com/products.php

Hope it was helpful!

You can try this: Kaspersky antirus for mobile phones on this link "http://software-files.download.com/sd/1oQcfRHKZhGhj4fcOWUAXvpZ4Toa4Gp_4FypACy3JWY7YKfpTwjAxth3MNoWUcWAkiAZq1WU1voBRTyH5y4tT8JOn7hMkdZ3/software/10640240/10640241/3/kavmobile_s602nd_v_6_0_70_en.sis?lop=link&ptype=1901&ontid=20&siteId=4&edId=3&spi=431f922c1192e78d65a601c860c4b344&pid=10640240&psid=10640241" or Norton antivirus on this link "http://www.freedownload3g.com/applications/upFiles/200904/Full-Norton-Antivirus.sis". Remember that once you get the antivirus installed on your phone you have to update it before it can serve to something.