It's not bad at all.
If you need, you must change tones and even story-leading style. Because readers may get bored of the same tone. I can explain this better, if you have experience of watching horror movies.
What happens there? Is the protagonist or central character always haunted or chased by some insatiable ghost or spirit?
No.
Horror stories do need scary scenes, but it won't do if the audience is always put up with frightening screenplay. Such is the way with books. You can start writing a science fiction, add slice-of-life or even fantasy and make your book no worse.
Actually, a change of tone, which mustn't be too frequent, might even better your scenes, if you are professional while doing it.
Let's take some examples.
Percy Jackson, a bestseller series, has the mixture of adventure, slice of life, comedy and even nostalgia. Harry Potter also has mixture of tones. Lord of the Rings doesn't change tones often, but it also isn't the same throughout the books.
But one thing can't be ignored. Don't change tones in an amateur way. Readers won't like it. Show to your readers the change is necessary and doesn't hurt the story or plot at all. Comedy is a good thing. Lord of the Rings is mostly serious, but now and then it does make you smile.
The last thing is, guess what your readers are expecting. Surprise them, since you're writing thriller. But if the surprise or turn of story is too unexpected for readers, then show logics and you may as well put obscure hints to make it more acceptable.