Shubham,
What you are experiencing is quite normal. While it may happen in small quantities with some men so that it is noticed, it may happen in small amounts to go unnoticed in some men.
When you are meeting your girlfriend, you are in a romantic mood and since there is some physical contact too, your body is preparing for sexual intercourse. While you say that you do not have any sexual thoughts in your mind, your body does not know where you are leading to and so prepares for the ultimate pleasure.
To get precum, you need not have an erection and just the presence of the opposite sex, is sufficient to give you sexual feelings. A number of things happen inside your body in response to sexual arousal. Your heart rate rises a bit and your blood pressure goes up. This leads to your penis getting bigger and depending on the amount of arousal, it will get erect. At the same time, preparations are made for the possibility of an ejaculation.
Two glands called the Cowpar's glands, begin producing a clear fluid that begins to drip out of the end of your penis. The purpose of this fluid is to push any possible remaining urine out of your penis. Urine is acidic and can kill sperm, so the body clears the pathway. If you feel the fluid, it is very slick. As it drips out of the end of the penis, it coats the end of your penis (the glans) to make it a bit easier to have sexual intercourse. That slickness also coats the inside of your urethra (the tube in your penis, so that when ejaculation occurs the semen has an easier time being shot out.
The production of the pre-ejaculate fluid is not one of those things you can control.
You should not get worried by this. This indicates you are healthy and your body is functioning normally.