When you 'keep something in mind' you aim to remember it or to be aware of it. If you 'have something in mind' means to have someone or something in your head or to be thinking of them. If you 'have someone in mind' you are thinking of someone who might be suitable for a particular responsibility or job. 

1. When you take your brother to the football match, please keep in mind that he is a lot younger than you, and will need looking after.
2. Please keep in mind that two of our guests are vegetarian when you are doing the food shopping.
3. It's worth keeping in mind a budget when you go shopping.

1. The head of our department thinks very highly of Harry. I believe he has him in mind for the vacant managerial position. 
2. I have someone in mind who will be able to design our posters.
3. I had Fran in mind to head that team. I think she would be very good at it.

1. The prospective client is a stickler for punctuality. My boss told me to keep that in mind before I went for my meeting with him.
2. Keep in mind that we can afford to make a loss on this contract if they agree to our other proposals.
3. Keep in mind that Robert is still on a probationary period if you are still dissatisfied with his output.