It definitely helps to know what part of the world the tree lives in as climate may have some bearing on tree health and possible pests differ from place to place. Knowing the location can take some of the guesses out of answers.
In this case, my best guess is the brown tips are from previous trimming. The larger brown bit in the middle almost certainly from previous scissor trim. Smaller brown tips probably the same.
When junipers are trimmed with scissors any needles that are cut in half turn brown at the ends.
How long have you had it? Have you done any trimming since having the tree?
