You have a massive project due at work, but the court demands your presence at 8 AM. Can you bring your laptop and knock out some spreadsheets while you wait to be called?
The rules change drastically depending on what room you are standing in.
In the Jury Assembly Room: Yes! Almost all modern courthouses allow you to bring a laptop, tablet, or smartphone into the main waiting area. In fact, they encourage it. You might be sitting there for 6 hours doing absolutely nothing. Many courts now offer free (albeit slow) Wi-Fi and designated workstations with outlets precisely so professionals can continue working.
In the Courtroom: Absolutely not. The minute your juror number is called and you line up to walk into an actual courtroom, all electronics must be powered completely off. You cannot use a laptop during voir dire (jury selection) or during a trial.
Bringing a laptop means going through courthouse security. You will have to take it out of your bag, just like at TSA. Do not bring bulky accessories, and be aware that certain courthouses (especially federal ones) have much stricter entry rules and may require you to check larger electronics at the door. Always check the specific court's website the night before.
You can usually work on your laptop in the main assembly room, but you must shut it down the second you are called into an actual courtroom. Bring a charger!