How come mobile phones dont need an anti virus when using the mobile internet on them ?

I have mobile internet on my phone. Its not like the full internet but you can check facebook on it and some other sites. Its on the meteor network which is an Irish mobile phone network here. But i notice with most phones there is no anti virus protection when browsing using your phone ?
Update: My phone is a nokia c1-01.
Is it because phones are less susceptible to viruses or something ?
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