My personal theory is yes. If not they should at least be able to feel when their passive buff items switch off
Can spellcasters automatically sense they're in an antimagic field?
I would think any character can tell when their magic items and active spells suddenly stop working.
Most magic has some sort of visual manifestation, but antimagic field is stated to be an invisible barrier so you can't see it.
However, despite this knowledge arcana checks should identify it since kn(arcana) says it can be used to identify spells in place.
Also, while optional rules:
Optional Ways to Acquire Spellblights
GMs may choose to include the following methods of acquiring spellblights.
Antimagic Field: The first time a spellcaster attempts to cast a spell within an antimagic field, there is a chance she will spontaneously gain a major spellblight. The caster must succeed at a Will saving throw (DC 15 + the caster level of the antimagic field or DC 23 if there is no caster level for the effect).
This implies you don't just automatically know when you're in an antimagic field.