If it's work related reading, something that you need to do in order to achieve the tasks given you by your lead, then it's fine.
It get's a bit more ambiguous if this is stuff you are expected to know - for example a programming language, calculus, or something of that sort. If that's the case, make sure your supervisor knows you are not proficient at those and doing the tasks will require learning on the job. At this point it's up to management to decide if they are OK with you doing the work or reassigning it to a person who is an expert in that field.
In my field that's normal practice - many people reference physics/mathematics books for formulas and our design docs often read like research papers with formulas being cited all over the place. If I'm asked to implement one of those algorithms it would be expected that I'll lookup all the formulas.