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Since it seems like you haven't

Always DARE never DEER with women

Illimitable Men Shit Test Encyclopedia

If you are in a casual situation I would keep it casual.

Women feed of validation of their attractiveness. It's survival.

You can say some shit like "Yeah I think about bending that ass over every second. I'm thinking it now slaps her ass, smirk, chuckle, escalate."

Imo that's indicative of a strong sexual frame.

Or "I think of you just as much as you me.".

Or "Who the fuck are you? Another stalker snuck in? BE GONE WENCH"

Psychological questions are usually either traps (see Vermillion's answer) or they are validation seeking. In this case, it is the latter. So, you have a lower quality woman trying to use you to validate her insecurities. "Validation" means to make her feel ok about her insecurities or reassure her that "everything is ok". For example, here she is worried that you are not devoted to her enough. She thinks of you when you are not around and worries that you do not do the same thing, thus making her feel like she might like you more than you like her, which makes her feel like she has less power over you, or even that you might leave her, making her even more insecure. "Validation" is when you say "Oh, I think about you all of the time" making her feel (1) more powerful in the relationship / more control over you, and (2) more secure because you are more devoted.

Here's the rule: NEVER VALIDATE

Another issue here is that she is asking you a question. That is bad in and of itself because when one person questions another, then the interrogator is assuming the superior role and the person being question is the subordinate. Obviously you do not want to allow her to be in a role where she is superior to you--it's disrespectful.

One way to deal with these kinds of questions is to not answer it directly but to say something related. For example, you could say: "I think about important things and that's what you should be doing as well." So, by saying this you are being responsive, but you are not actually answering her question (which would be submissive). Also, by saying "...that's what you should be doing as well" you are asserting dominance and showing leadership in the relationship.

This is a shit test. You can agree and amplify: yea babe literally all the time, I see your face on all the other girls.

Pressure flip: Bitch you think you're that special huh?

disagree and amplify: no never, actually I totally forget you even exist, it's like alzheimers

do you ever think of me when we aren’t talking

"Yep, sometimes".

or the fun option: "Who are you again?"

or the more extreme: "Of course I do Sara". (assuming her name isn't Sara)

or the nuclear option: "Which one are you again?"

Quite a few good answers already, so I'll just add my two cents: don't take her seriously. It's a dumb question, give it a dumb answer.

I'd go with something like "whenever I'm horny", or just a "meh" and not elaborating further. If she insists, change the subject. If she still keeps at it, ignore it and change the subject again - like you were never even talking about that bullshit. If she really keeps at it, or gets pissed, call her out on her behaviour "damn, next time I think about you, I'll remember how crazy you are". Just don't take stupid questions seriously.

(do you ever think of me when we aren't talking)

ya babe, just the other day I got a hard-on and thought why aren't you here to take care of this