The maiden selfie has been taken for a good cause as she was seen in the image, donning a T-shirt that said, "Hope and prayers for Andrew Wilson", reported Ace Showbiz.
Andrew Wilson is a 17-month-old boy battling Neuroblastoma, a form of cancer mostly found in infants and young children.
The 41-year-old actress is supporting his family by helping to raise money to cover medical and living expenses as Andrew undergoes treatment.
"This is my first selfie and it's for an amazing cause! Thank you all so much for helping support Andrew Wilson and his family," read the caption on the selfie by the "Training Day" actress.
It was not surprising that Mendes got actively involved in the cause as her brother Carlos is also battling the disease.