A teenager charged over the fatal stabbing of a Scientologist at the church's Sydney headquarters was trying to visit his mother who was undergoing a so-called purification ceremony, it has been revealed.

The 16-year-old is undergoing a mental health assessment after allegedly attacking a 24-year-old Church of Scientology member on Thursday at the organisation's Australasian headquarters in Chatswood.

NSW Police at the scene of a double stabbing at the Church of Scientology headquarters at Chatswood. Credit:AAP

The teenager, who police say also stabbed another man aged 30, was charged with murder, common assault (domestic violence), common assault, assault occasioning actual bodily harm and affray.

The accused was visiting the centre where his mother was to undergo a "purification ceremony", it is understood.