Surely you have to tell the people around you that you're meditating, or else they'll disturb you.
I'm aware that sounds around you become part of your meditation. But what happens when someone wants to talk to you? Two minutes of someone saying your name, followed by poking you, checking your breathing (unnecessary: you're already doing that yourself), and finally calling a first aider over because you aren't responding, is more than you're expected to take :-)
Once you tell your colleagues that you're meditating they might still think you look asleep but at least they'll know why you look that way. Either this is acceptable on work time or it is not. If it is then get on with it. If it's not then do it in your lunchbreak, before clocking on, make up the time at the end of the day, whatever your employer allows.
I have meditated at my desk on occasion, but only in a small office (3-4 people). I've also eaten lunch at my desk on occasion. Nobody stormed in and told me it wasn't allowed. My employers have always been happy for people to "clock off" and do their own thing at their desks. So people might watch video at lunch time, even play computer games.
Of course normally these activities are interruptible -- there's a natural assumption that if you're at your desk then you're available to communicate. That's why you need to explain this special case and pay attention to any negative feedback you get about it. There are workplaces and roles where meditation won't be permitted, or where it's totally inappropriate for you to be sat at your desk not working. Reception, for instance. Air traffic control ;-) I guess if you're even asking, you don't expect yours to be one of those. If in doubt ask your boss.