The idea of "perpetual motion" as an exceptional and unattainable condition is medieval, and relies on the notion that motion requires an energy input to be sustained.
That's a local truth. If you live at the bottom of a gravity well, with an atmosphere, and you are so completely under the influence of those things at all times that you don't even notice them, then such "laws of nature" as 'perpetual motion without an external force is impossible', or 'nature abhors a vacuum', are easy to demonstrate.
When you realise that the vast majority of everything IS vacuum, your perspective needs to change, or your ideas will become obsolete.
A spinning object in isolation will spin forever.
A planet is not entirely isolated, of course. Tidal effects from the Sun, Moon, and other planets and even distant stars and galaxies, all act to modify the rotation of the Earth. But the distances are large, gravity is weak, and the influence is inversely proportional to the square of the distance, so it will take a LONG time for any effects to become significant.
The tides slow the rotation of the Earth. Tne Moon is the largest tidal influence, because although it's small, it's very, very close by (in cosmic terms), at only half a million miles. The Sun is also a noticable influence; it's far away, but it's very large. No other object has an effect we can easily measure, or can detect without highly specialist equipment, over short timescales (and by 'short' I mean 'less than the time that human record keeping has existed').
So yes, in a sense, the spinning of an isolated neutron star is "perpetual motion", in that the motion will continue indefinitely.
But in the sense that the complete phrase "perpetual motion" implies an unknown and supernatural influence to counter the supposed natural tendency for all motion to stop, which is how the phrase is most commonly used in philosophy, it is an erroneous concept, based on the medieval mistake of ascribing local, (earthbound) conditions and observations to the universe as a whole.
Medieval observers saw the Moon and the Sun revolving around the world, and couldn't understand why they didn't slow down like everything else. Worse still, the planets occasionally did slow down, but then speeded up again! Trying to explain this led to all kinds of weird and arbitrary hypotheses (google "epicycles" if you want to know more about the knots these guys tied themselves in, trying to explain what they could see).
Three simple (but not at all obvious) ideas did away with the philosophical need for supernatural "perpetual motion"; The hypothesis that the universe is mostly vacuum; The hypothesis that the Earth is itself in motion, and not the fixed centre of the universe; And the hypothesis that an object in motion will continue in motion unless acted upon by a force.
As all moving objects near the Earth's surface are acted upon by forces applied by the air or water through which they move, and as we cannot feel the motion of the Earth, these three ideas were very hard to accept, and very difficult to demonstrate. But we now know them all to be the case. And, impressively, the likes of Copernicus, Galileo, Newton, and Kepler were able to demonstrate them before we had even achieved flight, much less spaceflight. Now we can actually go and see for ourselves that space is mostly vacuum - but we knew it before we went, just because of a handful of really impressive thinkers who were able to interpret the very mixed signals we were getting from our observations, which were the result of our abnormal situation: On a planet with an atmosphere, in orbit around a star, and orbited by a large and nearby Moon.
