The best mantra for anxiety as per Hinduism is being content and to stop searching for happiness in external things. Below is a mantra for anxiety and it should be chanted sitting facing east or northeast. It is also good to chant the mantra during sunrise.
Mantra For Anxiety
श्वेते वृषे समारूढा,श्वेताम्बरधरा शुचि:।
महागौरी शुभं दद्यात्,
महादेवप्रमोददाद।।
Shweta Vrishabe Samaruda Shwetambaradhara Shuchi
Mahagauri Shubhamddyat Mahadevpramoddath
Mahagauri Shubhamddyat Mahadevpramoddath
The meaning of the Mantra in Hindi:
सफेद वृषभ (बैल) पर सवारने वाली, श्वेत वस्त्र धारण करने वाली, सबसे पवित्र व महादेव को अपनी भक्ति से प्रसन्न करने वाली मां महागौरी हम सबका भला करो।