So~~ is that really necessary? some say virus' main target is win. but I just wanna check it out with you guys, please share some experience.~Thanks.
Not at this time. See:
Helpful Links Regarding Malware Protection
An excellent link to read is Tom Reed's Mac Malware Guide.
Also, visit The XLab FAQs and read Detecting and avoiding malware and spyware.
See these Apple articles:
If you require anti-virus protection I recommend using ClamXav.