Can a dog appear happy but be stressed at same time?

Just wondered please if anyone had any ideas. eg. a dog seems happy to see someone but then exhibits strange kind of behaviour, not aggresive.
Many thanks

A dog can be in conflict which someone who is used to observing dogs can detect, ie the dog wants to do something but is also afraid of something

perhaps it would help if you elaborated?

Thankyou I will try explain(bit complicated). Dog and owner are walking quite happily, just enjoying each others company, bit of ball throwing, bit of sit,stay etc. Then another dog walker they know comes along, the dog runs over to say hello because the person makes bit of fuss of them. The person starts talking to the dogs owner and the dog just changes, stars grabbing little sticks and chewing them up in kind of hyperactive way(?), eating berries, just kind of going off on one The dog is being told leave it but carries on, the owner has a theory that the dog is stressed in some way by the other persons presence. Sorry not very well explained.

Well it has had a lot of attention, this attention has now been removed.

Children behave in the same way.

Owner should give a command so that the dog knows what it is expected to do, eg down so dog lies down and relaxes.

Thankyou your help is much appreciated it's a bit difficult trying to explain the whole scenario very well, the owner is watching the dog and doesn't talk for ages, it can even happen in few seconds really. Even if the owner puts the dog on it's lead it still grabs at things, or just grass.

It could be displacement behaviour which would say the dog is conflicted but without actually seeing a) the behaviour and b) knowing other background it is difficult to say with absolute certainty.

Try reading about calming signals by Turrid Rugaas. It will open your eyes to all sorts of behaviours and indicators that you previously may not have noticed.

Thankyou I know it's difficult without actually seeing what's going on, i will look up about displacement behaviour. Turrid Rugaas certainly sounds interesting too, thankyou both.

Without seeing the dog its difficult, to me that sounds attention based,
dog knows that by doing that it will get back owners atention, this can of course be because its stressed because owner has switched off from it or it just know it works

Is it a collie?

It took a long time to get Daisy to accept people talking to me outside. She would get very upset. I stood at a good distance from them with her in a sit behind me, rewarding her when calm (onlead). With her it was about control of space. As a GSD she is happiest beside me but the incursion of a stranger was threatening.
She`s fine now.
My point being that the clue to the behaviour is probably in the dogs general attitude. What do you have problems with apart from this?